Characterization of spatial and temporal evolution of earthen sites construction technology in China based on GIS

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However, existing research has yet to provide a comprehensive quantitative analysis of the spatial and temporal evolution of construction techniques at earthen sites. This study identifies eight key techniques, including cut left, rammed earth, adobe, wattle and daub, cob, stacked earth, grass-wrapped mud, and mixed soil-rock structure. their evolution was delineated into five phases: (Ⅰ) Embryonic (Before 2070 B.C.), (Ⅱ) Development (2070 B.C.-221 B.C.), (Ⅲ) Formation (221 B.C.-618 A.D.), (Ⅳ) Application (618 A.D.-1206 A.D.), and (Ⅴ) Transformation (1206 A.D.-1911 A.D.). Spatial analysis using ArcGIS Pro tools uncovered a "concentration-diffusion" pattern: rammed earth techniques radiated from the Central Plains, stacked earth clustered along the Yellow and Yangtze Rivers, and cut left prevailed in early civilization regions. Quantitatively, cut left dominated the Embryonic phase (41.5%), while rammed earth usage escalated from 78.5% to 91.5% across subsequent phases, marginalizing other methods. By the Transformation phase, only four techniques persisted at 47 sites, with masonry and wood displacing earthen structures. The spatiotemporal evolution reflects dual drivers: natural factors (climate, soil, topography) and societal dynamics (productivity advances, demand shifts), epitomizing the dialectical human- environment relationship. This synthesis of technical progression and environmental adaptation not only clarifies historical construction practices but also informs contemporary strategies for heritage preservation. The findings underscore how ecological constraints and human ingenuity jointly shaped architectural innovation, offering vital insights for heritage conservation and historical research. Earthen sites Construction techniques Distributional characteristics Spatial and temporal evolution Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 1. Introduction Earth, as a fundamental building material, has played a pivotal role in the evolution of ancient architecture[1, 2]. "Earthen sites" is a broad term referring to the material remains of historical, artistic, scientific, social, and cultural value created by humans or associated with human activities, in which earth is the primary building material, and which have been preserved throughout human historical development[3, 4]. The construction of earthen sites has been influenced by various factors, such as the productivity levels of the era, the environmental conditions, and the functional needs, which together resulted in the development of distinct construction techniques[5-7]. Ivo Herle[8] provides a comprehensive examination of the development of raw earth construction internationally, while P. Doat and Gernot Minke detail a variety of earth construction techniques through an in-depth study of raw earth construction and its global literature[9]. John Norton further integrates modern concepts of raw earth architecture and analyzes the advancement of raw earth building techniques at a theoretical level[10]. The International Center for Raw Earth Architecture (CRATerre-ENSAG) in France has classified raw earth construction methods worldwide into twelve material-processing techniques, such as rammed earth, masonry, extrusion, molding, plastering, pressing, cutting, covering, and filling, as well as eighteen types of raw earth applications, including adobe, rammed earth, pressed earth bricks, straw mudballs, and wattle and daub[11]. In addition, The Guides de bonnes pratiques de la construction en terre crue , for the guidance of the restoration of new and old buildings, categorizes the techniques of raw earth into: les torchis, les briques de terre crue, le pies, la bauge, la terre allégée, les enduits en terre[12]. German archaeologists have created a vocabulary of the “cob balls, adobe, and daubed straw plaits” technique in four languages by investigating earthen architecture in Europe and Central Asia[13]. Some scholars have also systematically analyzed the technology of raw earth as a load-bearing body and wall covering[14]. The above study provides us with a basis for distinguishing between earthen buildings, archaeological sites and heritage buildings in our field survey. Therefore, it should be emphasized that the earth sites involved in this study refer to open-air building bodies with earth as the main building material and earth as load-bearing material, which have historical and cultural values. Due to its long history and vast geographical expanse, China is distinguished by a large number of earthen sites and a rich diversity of construction techniques[15]. Chinese archaeological and documentary data show that in the Paleolithic Age about 100,000 years ago, ancient humans dug caves and lived in them, and at this time, the main construction technology was digging and building in the raw earth. By the Neolithic Age (10,000 years ago - 5,000 years ago), the gradual emergence of ground construction, stacks of mud method wood and bone mud walls, and other technologies were applied by the ancients[16]. About 4,000 years ago, at the Longshan cultural site, the emergence of rammed earth construction for city walls, foundations, and other structures occurred[17, 18]. With the development of social productivity and the increase in demand, a wide variety of construction techniques based on rammed earth and adobe appeared in different regions and at different times across China. Techniques for constructing earthen sites have been well-documented in ancient China. Among these, the Song Dynasty (960 A.D.) in its "Methods of Construction" quantified the methods used in Chinese earthen buildings, leading to the establishment of specific architectural norms[19]. The "Standards of Architectural Engineering" from the Qing Dynasty (1616 A.D.) outlined operational procedures for earthen construction techniques[20]. Since the 21st century, Zhang has categorized Chinese earthwork construction methods into five types: cut left, rammed earth, cob, adobe, and earth block construction[17]; Pei classified earthen architectural construction techniques into five major categories and fifteen subcategories: cut left, stacked earth, rammed earth, adobe, and cob[21]. Based on a review of the literature and field investigations, this study categorizes earthen site construction techniques into eight types: cut left, stacked earth, rammed earth, cob, adobe, wattle and daub, mixed earth-rock structure, and grass-wrapped mud. In terms of the spatial and temporal evolution of construction technology, Pei[21], Xue[22], and Li[23] have conducted relevant studies on the Great Wall construction techniques, the evolution of earth-building methods, and the development and application of raw earth construction technologies, respectively. However, these studies were conducted regionally and have not addressed the issue on a national scale. Given that Chinese earthen sites span a long period, a large number of sites, and a vast geographical area, it is extremely challenging to analyze their construction techniques both temporally and spatially. Geographic Information Systems (GIS) offer a solution to these challenges due to their powerful ability to manage and analyze spatial data. Li [24] employed spatial analysis methods, such as Kernel Density Estimation (KDE) and trend surface analysis, to examine the spatial and temporal distribution of ancient Chinese archaeological sites and the factors influencing them. Li [25] explored the relationship between the spatial and temporal distribution of grottoes and the natural environment in Henan Province, China, using GIS for processing and visualization. Using GIS KDE, Du examined how population density affected the Ming Great Wall in Qinghai, China[26]. Chen et al. employed the GIS-FAHP method to map the freeze-thaw sensitivity of soil sites in China, considering the intensity of freeze-thaw conditions and the natural landscape variations [27]. These studies have demonstrated the strong performance of GIS in spatial analysis. However, current analyses of the evolution of construction techniques primarily involve literature reviews and generalizations, lacking visualization and quantitative analysis. Therefore, this study will utilize GIS to visualize and quantify the spatial and temporal evolution of construction techniques for Chinese earthen sites. This study compiles the construction histories and techniques of 553 state-protected earthen sites with well-documented construction methods. Through a review of the literature, these sites are categorized according to their historical periods. The spatial and temporal distribution, as well as the evolutionary characteristics of construction techniques, are then analyzed using KDE, the Center of Gravity Migration model, and Standard Deviation Ellipse (SDE) in GIS spatial analysis methods. Finally, the influencing factors behind the spatial distribution of construction techniques and the mechanisms governing their spatial and temporal evolution are explored. In essence, the temporal and spatial evolution of earthen site construction techniques results from the combined effects of geological environmental conditions and human social factors. Consequently, studying these techniques helps reveal the interconnected, interdependent, and interpenetrating relationship between humanity and nature, and is of significant engineering and historical importance. 2. Materials and Methods 2.1 Study area China, with its rich historical legacy and vast geographical expanse, is home to numerous earthen sites, which are distinguished by their long history, large number, extensive geographical distribution, significant cultural value, and diverse construction techniques. Thus, China has been selected as the focus of this study. According to data released by the State Administration of Cultural Heritage of China, there are 875 earthen sites included in the national key cultural relics protection list. Of these, 553 earthen sites have documented construction techniques and their respective construction periods. This study thus focuses on these 553 sites to examine the temporal and spatial evolution of construction techniques employed in Chinese earthen sites. 2.1.1 Types of construction techniques Through the collection and analysis of historical data on the construction techniques of earthen sites, these techniques can be categorized into eight distinct types: cut left, stacked earth, rammed earth, cob, adobe, wattle and daub, mixed earth-rock structure, and grass-wrapped mud. Fig. 1 illustrates the spatial distribution of the various construction techniques employed at the earthen sites. The specific data on the construction techniques and periods of the 553 sites are shown in Table 1. It should be noted that due to the lack of precise information on the generation breaks of some of the sites (it is only possible to determine the dynasty to which they belong). In order to ensure the scientific and comparable nature of the research data, this study uses the dynasty as the basic statistical unit. Table 1: Sites construction techniques and periods Periods/Techniques Adobe Mix soil-rock structure Cob Wattle and daub Stacked earth Rammed earth Cut left Grass-wrapped mud Prehistory (Before 2070 B.C.) 2 3 2 12 26 22 54 9 Xia, Shang and Zhou (2070 B.C. - 221 B.C.) 6 1 0 2 10 97 6 1 Qin and Han（including Wei and Jin） (221 B.C. - 618 A.D.) 12 6 0 2 7 107 2 0 Tang and Song (618 A.D. - 1206 A.D.) 5 2 1 1 1 107 0 0 Yuan, Ming and Qing (1206 A.D. - 1911 A.D.) 9 7 0 0 0 30 0 1 The authors have divided the construction techniques of earthen sites into pure earth techniques (rammed earth, stacked earth, cut left), mixed techniques (cob, grass-wrapped mud, wattle and daub, mixed soil-rock structures), and prefabricated technique (adobe). The reason for the separate distinction between adobe is that it differs significantly from the other technologies in sociological and anthropological terms. Specifically, the manufactured adobe is capable of being used by different people in different places. The technological characteristics of each technique are described below: (1) Adobe Adobe (Fig. 2a) is a technique in which blocks of the desired shape are made from loose soil through specific processing methods and then assembled into structures. The typical processing method for adobe involves mixing water with soil to create mud, reshaping the mud into blocks, drying them in the sun, and finally using the dried adobe blocks for masonry. Adobe masonry is generally divided into two main categories: The first involves shaping the blocks by hand according to the requirements of the structure or use, without the use of molds. The second category involves mixing the soil, placing it into a mold, pressing it into shape, and then drying it for use in masonry. In some regions, straw is added to the adobe bricks to increase their tensile strength. (2) Mixed earth-rock structure The mixed earth-rock structure (Fig. 2b) primarily involves the incorporation of stones or rocks into earthen ramparts or fortifications. Another important form of this construction technique is the use of clad brick walls as part of the earth-and-stone hybrid structure (A complete earthen structure (rammed earth, adobe) with an external layer of masonry on the inside). The key feature of this technique is the addition of stones or pebbles to the earth, which improves the structural integrity. Additionally, in some methods, alternating layers of earth and stone or large pebbles are used as a foundation base, which helps reduce the settlement of the earth by distributing the load more evenly. (3) Cob The primary materials for cob construction (Fig. 2c) are sand, water, and mortar, with straw and stalks often added to enhance the mixture. These materials are mixed and stacked to form walls. The specific method is to control the shape of the cob by hand; no other tools are used, and the surface is repaired after the main body of the cob is completed. It is important to emphasize that the shape of the cob is blocky so that cracks between the different cob blocks will be evident after drying. (4) Wattle and daub The wattle and daub method (Fig. 2d) involves using a wooden or bamboo frame as the skeleton, which is then woven and tied to form a three-dimensional mesh. Gaps in the structure are filled with a mud-and-grass mixture, enhancing the overall stability of the wall. This construction method also improves the thermal insulation and heat resistance properties of the building compared to traditional crypt-type housing. (5) Stacked earth Stacked earth (Fig. 2e) is commonly found in early earthen sites in southern China. In this region, due to the high clay and water content of the soil, direct ramming is not feasible. Preparation of the building can be accomplished by layering the soil along the height. There is no tamping process in this technique. (6) Rammed earth Rammed earth (Fig. 2f) involves compacting soil with specialized tools to increase its density and firmness, creating a solid structure through the application of external force. Rammed earth is one of the most widely used construction techniques in China's raw earth architecture. This technique can be further divided into two types: direct rammed earth and plate-rammed earth, depending on the specific construction method employed. Visible tamped layers and tamped nests are the key discriminatory criteria for identifying this technique. (7) Cut left Cut left (Fig. 2g) refers to a technique in which the exposed portion of the earth is excavated and used as the primary building material. The process generally involves first determining the building's layout and location, then excavating the surrounding soil, leaving the remaining earth in place to form the walls. This technique is used to create buildings such as houses and roads by utilizing the natural earth around them. (8) Grass-wrapped mud Grass-wrapped mud (Fig. 2h) is a construction technique used in wet environments, where a block of thatch or rushes is wrapped around soil and secured with plant fibers. This method is often found in primitive human dwellings. Its main advantages include high mobility, cost-effectiveness, easy availability of materials, and excellent thermal insulation properties. 2.2 Methods 2.2.1 Method of Dividing Construction Technology Stages Periodic classification is a method of categorizing artifacts according to the era in which they were produced. Each artifact can be traced back to a specific period, allowing for the classification of artifacts by their respective eras. By collecting and categorizing artifacts from the same period, it becomes easier to study the differences and developments between artifacts from various timeframes. Based on the chronological classification of artifacts from earthen sites, construction techniques are categorized according to the corresponding periods. Initially, data on the construction dates and techniques of state-protected earthen sites are collected. Subsequently, using the framework provided in the History of Ancient Chinese Architecture [28], the construction technologies of Chinese earthen sites are divided into distinct stages based on historical periods. 2.2.2 Methodology for characterization of spatial and temporal evolution All spatial analyses in this study were conducted exclusively using ArcGIS Pro 3.0. The China Geodetic Coordinate System 2000 (CGCS2000) was adopted as the geographic coordinate system, while the Gauss-Krüger projection served as the projected coordinate system. Statistics and plotting were performed using Excel 2021 and Origin 2025 software, respectively. The principles and formulas of the Kernel Density Estimation (KDE) and Standard Deviation Ellipse (SDE) method used in this study are all referred to in the help manual (ArcGIS Pro help—ArcGIS Pro | Documentation) and The ESRI guide to GIS analysis in ArcGIS Pro[29]. (1) Kernel Density Estimation Kernel Density Estimation (KDE) is a nonparametric statistical method that generates a continuous density surface by spreading the density contribution of each point to the surrounding area[30]. The core idea is to calculate the density contribution of each point to the surrounding area through the kernel function and determine the range of density diffusion through the search radius. In the field of cultural heritage, KDE is mainly used to reflect the degree of aggregation of sites[24]. Therefore, in this study, this method is used to analyze the spatiotemporal distribution characteristics of earthen site construction technology. The search radius directly affects the results of KDE. A radius that is too large or too small will lead to deviations in the results. In this study, the default search radius was used. The algorithm used to determine the default search radius (also known as the bandwidth) will perform the following operations: calculate the mean center of the input points; calculate the distances of all points to the mean center; calculate the median of these distances; calculate the standard distance. Then, the calculation is performed using the corresponding formula. For detailed procedures, see the ArcGIS Pro Help Manual. This method for selecting the search radius is based on the "Silverman Rule of Experience" bandwidth estimation formula. This method of calculating the default radius usually avoids the ring phenomenon around points that often appear in sparse data sets and prevents spatial outliers - that is, several points far away from the rest of the points[30]. Since the number and distribution range of the ruins sites in different periods are inconsistent, the calculated default radius is also different. If the radius is different, the absolute magnitude of the density value cannot be directly compared, but the spatial distribution pattern may still have reference value. If a unified search radius is used, it can ensure the comparability of the absolute density value, but it will result in over-smoothing of sparse data sets or under-smoothing of dense data sets. The above two cannot be satisfied at the same time. Therefore, in this study, the author adopts the method of unified search radius. Specifically, first, calculate the default search radius of each building technology separately and select the maximum recommended radius as the unified value. The calculation results show that the search radius of the wooden frame mud wall is the largest, which is 715534.855 m, which is the search radius of this study. In addition, the search range and output pixel are unified. The search range is the Chinese area, and the output pixel size is 9000×9000. For the five periods, the same method was adopted to determine a unified search radius for the kernel density estimation. Through calculation, the unified search radius was determined as 446543.454 m, while all other parameters remained consistent with the previous settings. (2) Directional Distribution (Standard Deviational Ellipses) A common method for measuring the trend for a set of points or areas is to calculate standard distances in the x, y, and z directions. These measurements can be used to define the axes of an ellipse (or ellipsoid) that encompasses the distribution of all features. Because the axes of the ellipse are defined by calculating the standard deviations of the x and y coordinates about the mean center, the ellipse is called a Standard Deviational Ellipse (SDE)[29]. This method is widely used to analyze the distribution and characteristic changes of geographical spatial elements[31, 32]. This study uses this method to analyze the distribution direction, dispersion degree, and central trend of different building technologies. 2.2.3 Methods of analyzing the factors influencing construction technology Earth site construction techniques are closely related to the environment (including climate, soil texture and topography) of the region in which they are located. Therefore, in this study, the vector dataset of annual average precipitation, soil texture and topography at the scale of 1:1,000,000 was obtained from the Resource Environment and Data Center of the Chinese Academy of Sciences ( https://www.resdc.cn/ ). The above data were analyzed by Overlay Analysis with site point data; precipitation, soil texture and geomorphology type attributes were accurately associated to each site point by using the Extract Multi Values to Points tool in ArcGIS Pro; and statistical analyses were subsequently performed to study the characteristics of the environmental elements of the different construction techniques. It should be noted that for the soil texture data, according to the classification criteria of the United States Department of Agriculture (USDA)[33], based on the difference in the proportion of content of the three grain groups of sand (2-0.05 mm), silt (0.05 - 0.002 mm), and clay (<0.002 mm), the soils were categorized as follows: Sand, Loamy Sand, Sandy Clay, Sandy Clay Loam. Sandy Loam, Clay Loam, Loam, Silty Loam, Silt, Silty Clay Loam, Silty Clay, Clay. Finally, the differences in soil texture between construction techniques were statistically analyzed. 3. Results 3.1 Stages of Construction Technology In this study, we first compiled the construction technologies and dynasties of construction for 553 earthen sites. Based on the historical development of ancient Chinese society, cultural exchanges, and advancements in construction technology, the evolution of earthen site construction can be divided into five stages: the embryonic stage, the development stage, the forming stage, the application stage, and the transition stage. The main characteristics of each stage are described in Table 2. 3.1.1 Embryonic stage The prehistoric period in China is classified as the embryonic stage of earthen site construction technology. Spanning from approximately before 2070 B.C., this period marks the transition of human habitation from caves to above-ground structures. The specific reference comes from the Dictionary of Chinese Archaeology [34]. The distribution of construction techniques during this period reflects the productivity levels and human needs of the time, as shown in Fig. 3a. The dominant construction methods were cut left (41.50%), followed by rammed earth (16.90%) and stacked earth (20%). The construction techniques of stacked earth and cut left were widely used in earthen sites in the early primitive period because they were relatively simple and required relatively low labor levels. For example, the Pengtoushan culture in the Yangtze River Basin (7500 B.C. to 6100 B.C.) had already seen the use of stacked earth and cut left[35]. During the same period, underground or semi-underground buildings were also discovered at the Jiahu cultural site in the upper reaches of the Huaihe River[36]. In the middle Neolithic period, at the Xinglongwa cultural site in northern China (6300 B.C.-5400 B.C.), the use of grass-wrapped mud appeared[37]. Three houses were discovered at the Dawenkou site in the lower reaches of the Yellow River in my country (4400 B.C.-2600 B.C.), which were built using the cob[38]. The earliest architectural site discovered so far that used wattle and daub construction technology should be the Miaodigou site in the middle period of the Yangshao culture (3900 B.C.-3600 B.C.). During the same period, the Zhengzhou Xishan site in the late Yangshao culture (3900 B.C.-2900 B.C.) showed the technology of rammed earth[39]. The earliest adobe construction technology discovered in my country is the Menbanwan site of the Qujialing culture (3300 B.C. to 2500 B.C.)[40]. The mixed earth-rock structure was used more in the early sites in mountainous areas. The technology appeared in the stone piles of the Miaodigou II culture (3400 B.C.-3100 B.C.)[41]. These technological advances not only reflect human adaptation to the environment but also signal progress in building techniques and social structures. 3.1.2 Developmental stage During the Xia, Shang, and Zhou dynasties (2070 B.C. - 221 B.C.), societal shifts from clan-based communal ownership to private family ownership resulted in heightened social differentiation and the formation of hierarchies. This period witnessed significant advancements in earthen site construction techniques, closely linked to improved productivity and the expansion of human needs. The construction of city walls for defense and the rise of high-platform buildings- often with rammed earth foundations- served both practical and symbolic functions, representing social status and ritual significance. As seen in Fig. 3b, the use of cut left and stacked earth methods decreased to 5% and 8%, respectively, as these techniques could no longer meet the growing demands for strength and durability. Conversely, the proportion of rammed earth constructions increased significantly to 78.9%, reflecting the evolution of social structures and the advancement of construction technologies. 3.1.3 Forming stage The Qin-Han period (including the Wei and Jin dynasties) (221 B.C. - 618 A.D.) saw the establishment of a centralized power system as society transitioned from slavery to feudalism[42]. This period marked significant developments in earthen site construction, fueled by increased productivity and growing human needs. Construction techniques became more refined, particularly with the advent of preparation techniques and the rammed-earth plate construction method. Advances in materials such as bamboo, grass, reeds, and hemp ropes played a crucial role in enhancing rammed earth technology. City walls were built not only for defense but also to symbolize ritual status and power, often elevated on rammed earth foundations[43]. Similarly, the palace buildings of the ruling class began to adopt a combination of rammed earth, adobe, and timber-framed techniques to achieve both aesthetic and functional effects. During this period, 78.7% of earthen sites employed rammed earth, while the use of adobe increased to 8.9%. In contrast, the use of cut left and wattle and daub techniques declined to 2% (Fig. 3c). The earthen site construction process began to take its current form, with rammed earth becoming the dominant technique. 3.1.4 Application stage During the Tang and Song dynasties (618 A.D. - 1206 A.D.), the use of rammed earth construction techniques further increased, accounting for 91.5% of the total. Conversely, the use of stacked earth, wattle and daub, and grass-wrapped mud techniques declined, with stacked earth representing only 1% (Fig. 3d). This period saw minimal use of cut left techniques, while adobe construction became more widespread, often in combination with rammed earth. This shift reflects the diversification and advancement of earthen site construction techniques. 3.1.5 Transition stage By the Yuan, Ming, and Qing dynasties (1206 A.D. - 1911 A.D.), brick and wood structures became the dominant construction methods[44]. During the Yuan Dynasty, wooden structures were simplified and became a significant architectural form in China. The development of brick-making technology and lime-based bonding materials led to the widespread use of masonry techniques in palaces, temples, and other buildings. Although the number of earthen sites decreased during this period, earthen construction techniques continued to be used, though in more refined forms. A typical example is the Ming Great Wall, which still stands today. During this period, earth tamping remained the primary technique (Fig. 3e), but the overall number of state-protected earthen sites declined, reflecting the broader trend of transitioning from earthen to wood and masonry construction techniques. Table 2: E arthen heritage sites process stages Construction techniques periods Characteristics of the periods Embryonic stage (Before 2070 B.C.) prehistory A variety of construction techniques were successively produced, the process is relatively primitive and simple, with the highest proportion of cut left. Developmental stage (2070 B.C. - 221 B.C.) Xia, Shang and Zhou The economic system of clan communal ownership was gradually replaced by family private ownership, the development of productivity, defensive attributes of the city wall, ritual attributes of the high platform building began to appear, and the process of rammed earth began to gradually become the mainstream process. Forming stage (221 B.C. - 618 A.D.) Qin and Han The development of the earthen site construction process took shape. The development of sophisticated hemp cordage techniques contributed to the advancement of rammed earth construction. The adobe process gradually developed from unmolded adobe to standardized molded adobe. Application stage (618 A.D. - 1206 A.D.) Tang and Song The combined use of various earthen site construction techniques has increased, and the construction process has gradually become scientific and rationalized. Transition stage (1206 A.D. - 1911 A.D.) Yuan, Ming and Qing The number of earthen sites has declined, and there has been a gradual shift to masonry and wood construction for the dominant site-building techniques. 3.2 Characterization of the spatial distribution of construction techniques at earthen sites 3.2.1 Characteristics of the overall distribution of construction technologies As shown in Fig. 1, China's earthen sites are mainly distributed in the Yellow River Basin and the Central Plains, the northwest arid area, the Yangtze River Basin and the southern region, and the northeast region; a small number are distributed in the Qinghai-Tibet Plateau and the southwest region. Analyzing the preservation status of the sites reveals that these technologies are concentrated mainly in the central and northern regions of China. Specifically, the cut left technique is predominantly found in the middle and upper reaches of the Yellow River Basin, while stacked earth is mainly distributed in the middle and lower reaches of the Yangtze River, areas characterized by a humid climate and high rainfall. Adobe is widely used in Xinjiang, and the core distribution of rammed earth extends along the Yellow River Basin. The distribution of other construction techniques is less pronounced. 3.2.2 Characteristics of the distribution of different construction technologies In this study, six construction techniques ( rammed earth , stacked earth, wattle and daub, adobe, grass-wrapped mud, and cut left) were selected for spatial KDE. The cob and mixed earth-rock structures were excluded from the analysis due to the limited number of site locations associated with these methods. Based on the kernel density distribution, the spatial distribution characteristics of various construction techniques are described as follows. As shown in Fig. 4a, as the dominant construction technique, rammed earth is widely distributed throughout the country, and its core area is located in the Central Plains, which is the center of ancient China's economy and politics. Stacking earth technology is mainly distributed in the Yangtze River Basin in southern China, and a small amount appears in Northeast my country (Fig. 4b). Cut left technology is concentrated around the Yellow River Basin, and the highest distribution density is in the Loess Plateau (Fig. 4c). Grass-wrapped mud technology is mainly distributed in the Yellow River and Yangtze River Basins, and is scattered in southwest China and Xinjiang (Fig. 4d). Wattle and daub have a dual-core distribution, concentrated in the two river basins in eastern my country and southern Xinjiang (Fig. 4e). Adobe bricks are distributed in a belt along the ancient Silk Road, extending from the Hexi Corridor to western Xinjiang (Fig. 4f). 3.3 Key Influencing Factors of Earthen Heritage Construction Techniques Soil texture, which refers to the relative proportions of different particle sizes in the soil, plays a critical role in determining the physical properties of the soil and significantly impacts the use of raw soil materials in construction. In this study, the U.S. soil texture classification system was used, with the content of clay (<0.002 mm), silt (0.002-0.05 mm), and sand (0.05-2 mm) particles represented in triangular coordinate graphs, as shown in Fig. 5. The results reveal that sandy clay loam was the preferred soil type for the construction techniques of adobe, mixed earth-rock structures, cob, and grass-wrapped mud. In contrast, the stacked earth technique tends to favor clay loam soils. Soils with moderate amounts of clay and sand, such as sandy loam and clay loam, are typically used for techniques such as cut left, wattle and daub, and rammed earth. In particular, the rammed earth technique is used in an area with a wide range of soil types. 4. Discussion Numerous studies have demonstrated that the spatial and temporal evolution of construction techniques at earthen sites is closely linked to natural, human, and technological factors[45]. Natural elements, such as climate, soil quality, and topography, form the geographical conditions that influence the application of construction techniques. Human elements, including production activities, social structure, and cultural customs, serve as the driving forces behind the demand for these technologies. Technological elements, such as the economic and technical capabilities of the builders, set the conditions under which these construction techniques develop. In the early stages of applying raw soil construction techniques, people underwent a trial-and-error process, adapting to local natural conditions to find the most suitable building methods that would meet production and living needs. Once a particular architectural form, technical system, or construction process gained general acceptance in a region, it was widely replicated. As economic and technological capabilities improved, people’s evolving material and spiritual needs led to further advancements and refinements in existing techniques, systems, and processes, often driving innovation[46]. 4.1 Factors influencing the spatial distribution of construction technologies Natural factors, which form the basis of construction technologies, significantly influence the spatial distribution of these techniques. To explore this, this study analyzes the impact of climate, soil quality, and topography in the areas where the selected earthen sites are located, using statistical data. 4.1.1 Climatic factor Climatic differences, particularly variations in rainfall, have had a profound impact on the development of construction techniques at earthen sites. China can be divided into several climatic zones based on annual precipitation: arid (1200 mm) (Fig. 6). Statistically, the proportion of adobe construction is highest in the arid zone at 81 %, while stacked earth is predominantly found in humid and wet zones, accounting for about 82 % in these regions. Other technologies are predominantly found in semi-humid zones (Table 3). Climatic conditions have influenced the creation of these construction techniques from the outset[47]. The origins of construction methods differ between the Yellow River Basin and the Yangtze River Basin. In the Yangtze River Basin, characterized by low-lying terrain, a hot and humid climate, and a dense water network, nest dwellings developed in lake and swamp areas. These regions, rich in water and natural resources, were ideal for early human settlements based on fishing, hunting, and gathering[48]. In this environment, elevated dwellings made from wooden materials emerged, as the region lacked natural caves. Conversely, the Yellow River Basin, with its dry climate and loess-rich soil, saw the development of cave dwellings-specifically loess cave dwellings- which were more suitable to the area's low rainfall[49]. In the arid region of Xinjiang, characterized by very low annual precipitation, the cut left construction technique was developed. The region's low rainfall meant that rainwater erosion had minimal impact on the exposed parts of the earth, allowing buildings constructed with this technique to be better preserved over time. With the passage of time, the rammed earth construction technique gradually became the primary method for building earthen structures, spreading throughout China. However, there are regional variations in rammed earth technology. In northern regions, where the primary need is for heat preservation and protection against cold winters, rammed earth walls are thicker. This method typically involves the rafter-building technique, and when the plate-building technique is used, smaller plywood sizes are employed, with internal wooden pillars supporting the walls. In contrast, in southern regions, where moisture protection and heat resistance are more critical, rammed earth walls are thinner, and the plate-building method is more commonly used. Here, the plywood used is longer, and bamboo reinforcement is often added to increase wall stability, with additional efforts to seal the walls [50, 51]. These differences underscore the adaptation of building techniques to the specific climatic needs of each region. Table 3: Percentage of sites in different climatic zones Zones/Techniques Adobe Mix soil-rock structure Cob Wattle and daub Stacked earth Rammed earth Cut left Grass-wrapped mud arid (<200 mm) 35 (81 %) 3 (23 %) - 5 (29 %) 1 (2 %) 28 (8 %) 2 (4 %) 1 (8 %) semi-arid (200-400 mm) 2 (5 %) 3 (23 %) - - 2 (5 %) 59 (16 %) 9 (15 %) 1 (8 %) semi-humid (400-800 mm) 5 (12 %) 6 (46 %) 1 (50 %) 7 (41 %) 5 (11 %) 216 (59 %) 42 (74 %) 8 (68 %) humid (800-1200 mm) 1 (2 %) 1 (8 %) 1 (50 %) 3 (18 %) 19 (43 %) 34 (9 %) 3 (5 %) 1 (8 %) wet (>1200 mm) - - - 2 (12 %) 17 (39 %) 28 (8 %) 1 (2 %) 1 (8 %) 4.1.2 Soil factor Soil texture directly determines the feasibility, technical complexity, and preservation duration of earthen site construction techniques. The regional soil types corresponding to adobe construction, mixed earth-rock structures, and cob techniques predominantly consist of sandy clay loam. This particular soil composition helps minimize cracking during drying processes while enhancing structural strength[52-54]. These techniques are primarily concentrated in Northwest China where soils exhibit higher proportions of sand and silt. The stacked earth technique predominantly occurs in southern China characterized by clay loam soils. This preference arises from their elevated clay content (>30%) and cohesive properties that facilitate molded construction through stacking[55]. Cut left techniques are mainly distributed across the Loess Plateau with sandy loam soils, where the soil's excellent integrity and moderate plasticity allow cave dwelling excavation using simple tools[56]. Both grass-wrapped mud techniques and wattle and daub constructions are associated with sandy loam and clay loam soils. These two techniques directly manifest ancient craftsmen's structural innovations: the former enhances soil erosion resistance, while the latter prioritizes functional and structural stability[23]. Rammed earth techniques predominantly utilize sandy loam and clay loam soils, though their application extends to diverse soil types, demonstrating exceptional geographical adaptability. Modern studies on rammed earth structures reveal that particularly sandy loam can form dense, monolithic, and structurally robust walls through compaction processes[57]. Most Chinese regions possess soil conditions suitable for rammed earth construction when appropriately modified with fine sand or other amendments, explaining its status as China's most widely distributed construction technique[58]. Furthermore, rammed earth technology exemplifies ancient Chinese artisans' material modification expertise. Specifically, northwestern builders incorporated tamarisk branches (enhancing tensile strength) and coarse sand (reducing drying shrinkage)[22], while southern innovators utilized organic additives like glutinous rice mortar (improving cohesive strength) and egg white (forming hydrophobic membranes), enabling rammed earth applications even in humid regions with annual precipitation exceeding 800 mm[45]. Through a tripartite adaptive mechanism of "local material selection – performance enhancement – structural innovation", ancient craftsmen transformed soil limitations into technical features (e.g., loess cave dwellings, reinforced earth walls), demonstrating profound understanding and creative utilization of natural materials. This soil-property-driven technological diversity provides significant material science and engineering insights for contemporary earthen heritage conservation. 4.1.3 Topographic factor Topography plays a crucial role in the development of earthen site construction techniques. Different topographic features often determine the shape of the earthen site, which in turn drives the adoption of suitable construction methods. According to The Standard for 1:1,000,000 Geomorphological Mapping of China (Provisional) [59], China's landforms can be systematically classified into seven categories based on relief amplitude: Plain (<20 mm), Platform (20-30 mm), Hills (30-200 mm), Low-relief Mountainous Terrain (200-500 mm), Moderate-relief Mountainous Terrain (500-1000 mm), High-relief Mountainous Terrain (1000-2500 mm), Extremely High-relief Mountainous Terrain (＞2500 mm)[60]. Relief amplitude is defined as the vertical elevation difference between a mountain ridge (summit) and either the nearest major river (with a drainage area exceeding 500 km²) along the downslope direction or the closest junction point with a broader plain/platform (width >5 km). In terms of national topography, architectural techniques exhibit a clear distribution pattern influenced by the differences in terrain and geomorphology. Of the national heritage sites with detailed topographic and geomorphologic data, 553 sites were analyzed. Of these, 343 (62%) are located on plains, 113 (20%) on platforms, 52 (9%) on hills, 24 (5%) on low-relief mountainous terrain, and 21 (4%) on medium undulating mountains (Fig. 7 and Table 4). Earthen sites are predominantly concentrated in plains. This is largely because the flat and open nature of plains imposes fewer restrictions on construction techniques. In contrast, the relief mountainous terrains have a higher proportion of mixed earth-rock structures. This can be attributed to two factors: first, areas with significant terrain variation require additional materials, such as stone, to stabilize foundations; second, due to local material constraints, builders often need to select and utilize available resources based on the local environment. Table 4: Percentage of sites in different landscapes Geomorphology (Relief Amplitude)/Techniques Adobe Mix soil-rock structure Cob Wattle and daub Stacked earth Rammed earth Cut left Grass-wrapped mud Plain (<20 mm) 34 (79 %) 9 (69 %) 1 (50 %) 13 (76 %) 28 (64 %) 228 (62 %) 25 (44 %) 5 (41 %) Platform (20-30 mm) 5 (12 %) 1 (8 %) 1 (50 %) 2 (12 %) 9 (20 %) 78 (21 %) 14 (24 %) 3 (25 %) Hills (30-200 mm) 3 (7 %) - - 2 (12 %) 2 (5 %) 31 (8 %) 12 (21 %) 2 (17 %) Low-relief Mountainous Terrain (200-500 mm) - 1 (8 %) - - 5 (11 %) 16 (4 %) 2 (4 %) - Moderate-relief Mountainous Terrain (500-1000 mm) 1 (2 %) 2 (15 %) - - - 12 (3 %) 4 (7 %) 2 (17 %) High-relief Mountainous Terrain (1000-2500 mm) - - - - - - - - Extremely High-relief Mountainous Terrain (＞2500 mm) - - - - - - - - 4.2 Mechanism analysis of the spatial and temporal evolution of construction technology To analyze the spatial and temporal distribution characteristics of earthen site construction techniques, this study divides the historical periods of the development of nationally protected earthen sites with different construction techniques into five time periods: the prehistoric period (Before 2070 B.C.), the Xia, Shang, and Zhou periods (2070 B.C. - 221 B.C.), the Qin and Han periods (221 B.C. - 618 A.D.), the Tang and Song periods (618 A.D. - 1206 A.D.), and the Yuan, Ming, and Qing periods (1206 A.D. - 1911 A.D.). These periods correspond to the stages of development of construction techniques for earthen sites. 4.2.1 Characteristics of the spatial and temporal evolution of construction technology During the prehistoric period , human society had low productivity and relatively simple activities, leading to earthen site construction technology being mainly concentrated in the Yellow River and Yangtze River Basins. Specifically, the cut left technique was predominantly found in the middle and upper reaches of the Yellow River and the southwestern part of Northeast China. The stacked earth technique was mainly concentrated in the central Yangtze River Basin, while rammed earth was widely used in the middle and lower reaches of the Yellow River Basin (Fig. 8a). This period marks the area where ancient humans largely settled and is considered the cradle of Chinese civilization. During the Xia, Shang, and Zhou periods , as China transitioned from primitive society to slave society, the spatial distribution of earthen site construction techniques became more centralized, correlating closely with the scope of economic activities of the time. The cut left technique was drastically reduced, showing a sporadic, point-like distribution. Rammed earth was widely spread, primarily in central Shaanxi, northwestern Shanxi, southern Hebei, and Shandong, while stacked earth remained concentrated in the lower reaches of the Yangtze River. The latter technique was heavily influenced by the local environment and proved well-suited to the humid, rainfall-rich southern regions (Fig. 8b). The Qin-Han period , which included the Wei, Jin, and Northern and Southern Dynasties, was marked by frequent warfare in Chinese history. During this period, the distribution of earthen site construction techniques became more extensive, with two core areas centered around Xi'an and Luoyang . Additionally, a belt-shaped distribution formed along the Ancient Silk Road , from the Hexi Corridor to Xinjiang , reflecting the increasingly close social and cultural exchanges as Chinese civilization expanded. The distribution of construction techniques mirrored this expansion (Fig. 8c). By this time, the cut left technique had almost disappeared, while rammed earth continued to be widespread. The adobe technique also became more common, particularly in the Xinjiang region. By the Tang and Song dynasties , China experienced a period of economic prosperity and stability. Wood and masonry construction techniques had matured, partially replacing traditional earthen techniques. Nevertheless, earthen site construction technologies particularly rammed earth , continued to be widely distributed due to their standardization and ability to integrate well with wood and masonry structures. These techniques were concentrated primarily in the middle and lower reaches of the Yellow River, northeast China, and Xinjiang (Fig. 8d). In the Yuan, Ming, and Qing dynasties , the number of state-protected earthen sites declined significantly, reflecting the gradual replacement of earthen construction technologies by masonry and wooden structures. However, rammed earth construction remained dominant, even though its geographical distribution became more dispersed (Fig. 8e). This shift in construction techniques was driven by the advancements in masonry and wood construction methods, which gradually replaced traditional earthen methods. 4.2.2 Analysis of the directionality and center of gravity shift of construction technology in different historical periods By analyzing the SDE across five historical periods, we can gain insight into how the orientation and distribution of earthen site construction techniques evolved over time. As shown in Fig. 9 , from the prehistoric period to the Xia, Shang, and Zhou periods , the azimuth of the SDE changed from 76.06° to 109.75°. In the prehistoric period, the center of gravity of earthen site construction technology was located in the northern part of Henan Province . This is because the region (the Yellow River Basin) is the birthplace of Chinese civilization. During the Xia, Shang, and Zhou periods , this center of gravity shifted northwest along the Yellow River by 90.18 km. The shift in the center of gravity during the Xia, Shang, and Zhou periods, on the other hand, can be attributed to the establishment of state power, which led to a reorientation of construction technology and a concentration of activity toward the north. In concrete terms, the capitals of the Xia and Shang dynasties were both located in present-day Henan Province, while the capital of the Zhou Dynasty migrated to Shaanxi Province, northwest of Henan[61]. This could plausibly explain the migration of centers and the change of direction. In addition, the distribution of earthen sites is small due to the constraints of primitive technological capabilities and the limited scope of civilization. During the Qin and Han dynasties , the center of gravity shifted significantly to the northwest by 426.59 km, and the azimuth of the SDE changed to 108.87°, showing a northwest-southeast orientation with greater spatial dispersion. This shift is closely linked to the rise of the Silk Road and the corresponding changes in political and economic centers. Cultural exchanges and nomadic pressures from the north synergistically drove the spatial expansion of earthen sites in that direction. Specifically, the opening of the Hexi Corridor and the rise of the Silk Road during the Han Dynasty are strong evidence of this[62]. By the Tang and Song dynasties , the azimuth of the SDE was adjusted to 76.92°, and the spatial distribution pattern shifted to a southwest-northeast direction. The center of gravity moved northeastward by 498.53 km. The expansion of the territorial area and the reduction of conflicts on the western borders contributed to the shift in the direction of the distribution of earthen sites (northeast-southwest) and the expansion of their area. In present-day northeastern China, the Tang Dynasty fought many large-scale wars with the Gouryeo and Balhae can explain the change in the direction of distribution and the migration of direction[63]. In the Yuan, Ming, and Qing dynasties , the center of gravity shifted southwest by 439.33 km. The azimuth of the SDE becomes 102.58°. The intensification of border conflicts in the northwest and the stabilization of the eastern part of the country led to a reorientation of the distribution towards northwest-southeast. The Ming dynasty's construction of nine border towns, repair of the Great Wall, and the stationing of heavy troops to deal with the nomadic forces in the northwest by strong military means are direct evidence of this[64]. The changes not only reveal the spatial distribution characteristics of earthen site construction technology but also reflect how socio-political and economic factors influenced technological development in different historical periods. Table 5: Variation of SDE parameters of earth heritage sites construction technology in different historical periods periods center of gravity coordinate L1 long axis（km） L2 short axis（km） azimuth（°） migration distance（km） direction of migration Prehistoric 112°21′42″E 34°53′31″N 760.31 592.55 76.06 - - Xia, Shang and Zhou 113°38′16″E 34°59′42″N 892.71 580.31 109.75 90.18 northwest Qin and Han 105°07′01″E 36°29′06″N 1406.11 693.82 108.87 426.59 northwest Tang and Song 110°19′46″E 39°44′09″N 1501.31 937.57 76.92 498.53 northeast Yuan, Ming and Qing 104°54′08″E 38°50′13″N 1579.36 939.92 102.58 439.33 southwest 5. Conclusion Based on the data of the national key protection earth sites, this study summarizes the earth site construction techniques into eight categories based on the prior research. The development of these techniques is divided into five stages: embryonic, developmental, formative, application, and transformation. Each stage evolved in response to shifts in productivity levels and the social environment, reflecting broader societal transformations. These construction methods arise from the interaction between human ingenuity and natural conditions, embodying the collective knowledge of the workforce. (1) In the embryonic stage, the cut left technique was predominant, accounting for 41.5% of total usage. In the developmental stage, the prevalence of cut left and stacked earth decreased, while rammed earth increased substantially to 78.9% due to its superior strength and spatial advantages. During the formative stage, rammed earth constituted 78.7% of the total, adobe increased to 8.9%, and the proportion of cut left and wattle-and-daub decreased to 2%. In the application stage, the cut left technique disappeared, and rammed earth increased to 91.5%. The use of adobe expanded, often in combination with rammed earth and other techniques, demonstrating the versatility of earthen construction methods. The transformation stage marked the decline of traditional earthen construction, with a shift toward brick and wooden structures, signaling a major technological change in construction practices. (2) The spatial distribution of earthen architectural techniques in China exhibits regional differentiation characteristics shaped by synergistic interactions between natural and anthropogenic factors. Within the climate-soil coupling mechanism, the arid northwest region (annual precipitation 800 mm) developed stacked construction techniques (82%) through cementation processes in high-clay soils (>30% clay content). The semi-humid Central Plains (precipitation 400-800 mm) emerged as a concentration zone for rammed earth architecture (59%), benefiting from optimal loam textures and the geographic location of the civilizational core. Because of the simplicity of the process, its high strength, and the universality of the improved soil, the rammed earth technique is widely used throughout the country. Topographically, plains account for 69% of sites, reflecting construction advantages of flat terrain, while unique geomorphologies like loess tablelands fostered cut left techniques. This technological-geographical variation essentially represents ancient craftsmen's adaptive innovations in response to regional soil-climate systems. (3) The spatiotemporal evolution of Chinese earthen construction techniques exhibits a dynamic "concentration-diffusion" pattern, with axial shifts closely correlated to historical geopolitical transformations. During the prehistoric to Xia, Shang, and Zhou periods, constrained by primitive technical capabilities and limited civilizational boundaries, these techniques were initially developed along the Yellow and Yangtze River basins. Subsequently, the Qin-Han periods witnessed a northwest-southeast axial rotation aligned with Silk Road development, where cultural exchanges and nomadic pressures from the north synergistically drove spatial expansion along this direction. The Tang-Song period saw a strategic reorientation to a northeast-southwest distribution pattern, propelled by territorial expansion and reduced Western frontier conflicts, which facilitated both directional shifts and spatial extension. Ultimately, during the Yuan-Ming-Qing periods, intensified northwestern frontier conflicts coupled with eastern regional stabilization reconfigured the distribution axis back to a northwest-southeast orientation. Although this study offers valuable insights, it is limited by the relatively small number of state-protected earthen sites, which may constrain the comprehensiveness of its findings. Future research will extend the analysis to include provincial and county-level protected earthen sites. 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Liu, et al., Dynamic Characterization of a Reinforcement Rammed Wall for the Earthen Ruins, Shock and Vibration, 2022 (2022). https://doi.rog/10.1155/2022/3439431 I.o.g.s.a.n.r. reserch, The Standard for 1:1,000,000 Geomorphological Mapping of China (Provisional) (in Chinese), Science Press, Beijing, 1987. B.Y. Li, B.T. Pan, J.F. Han, Discussion on the basic landform types and their classification indexes in China (in Chinese), Quaternary Research, (2008) 535-543. https://doi.rog/10.3321/j.issn:1001-7410.2008.04.004 Q.Z. Liu, Archaeological Interpretation of the Continuity of Chinese Civilization over Five Thousand Years, Frontiers of History in China, 17 (2022) 537-588. https://doi.rog/10.3868/s020-011-022-0023-3 D.L.-m.Z. DeFalco, The Silk Road in China, California State University, California, 2007. N.N. Liu, A view on the policy of Sui-Tang Dynasties on Gouryeo, Balhae and the Turkic factors (in Chinese), in, Yanbian University, Yanji, 2017. T. Fang, A study of the borderland administrative systems of the Yuan,the Ming and the Qing dynasties (in Chinese), Journal of Yunnan Minzu University(Philosophy and Social Sciences Edition), 33 (2016) 79-84. https://doi.rog/10.13727/j.cnki.53-1191/c.2016.01.013 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 13 Jun, 2025 Read the published version in Archaeological and Anthropological Sciences → Version 1 posted Editorial decision: Revision requested 24 Apr, 2025 Reviews received at journal 10 Apr, 2025 Reviews received at journal 08 Apr, 2025 Reviewers agreed at journal 08 Apr, 2025 Reviewers agreed at journal 08 Apr, 2025 Reviewers invited by journal 08 Apr, 2025 Submission checks completed at journal 07 Apr, 2025 First submitted to journal 05 Apr, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-5813558","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":447600676,"identity":"b1d3a643-b167-48af-aea9-08b73a1631c7","order_by":0,"name":"Zhiqian Guo","email":"","orcid":"","institution":"Lanzhou University","correspondingAuthor":false,"prefix":"","firstName":"Zhiqian","middleName":"","lastName":"Guo","suffix":""},{"id":447600677,"identity":"2350c596-bc02-4a3a-aab1-fe6a3e4923b9","order_by":1,"name":"Qiang Qi","email":"","orcid":"","institution":"Lanzhou University","correspondingAuthor":false,"prefix":"","firstName":"Qiang","middleName":"","lastName":"Qi","suffix":""},{"id":447600678,"identity":"45982a9d-8df9-4c8e-9599-145be4698125","order_by":2,"name":"Shuai Zhang","email":"","orcid":"","institution":"Lanzhou University","correspondingAuthor":false,"prefix":"","firstName":"Shuai","middleName":"","lastName":"Zhang","suffix":""},{"id":447600679,"identity":"4f6bee8e-f1af-402d-802f-dbfc45c12a93","order_by":3,"name":"Wenwu Chen","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAuUlEQVRIiWNgGAWjYNCCCgswJUGCljMSpGphbCNFi/yM3MOvC+dJ2BscYD54m4fBLo+gFoMbeWnWM7dJMBscYEu25mFILiasRSLHzJh3mwSbwQEeM2kehgOJDYQdBtIyR4LH4AD/N+K0MNzIMX7M2yAhAbSFjTgtBmfemDHPOCZhIHmYzdhyjkEyEQ5rzzH+XFBjY893vPnhjTcVdkQ4jIGBTRpMMYMtJUI9SO1n4tSNglEwCkbBiAUAjBsygwLxuB4AAAAASUVORK5CYII=","orcid":"","institution":"Lanzhou University","correspondingAuthor":true,"prefix":"","firstName":"Wenwu","middleName":"","lastName":"Chen","suffix":""},{"id":447600680,"identity":"4a2f8756-8857-45fc-8a4f-ad9e48ead49f","order_by":4,"name":"Lei Yang","email":"","orcid":"","institution":"Lanzhou University","correspondingAuthor":false,"prefix":"","firstName":"Lei","middleName":"","lastName":"Yang","suffix":""},{"id":447600681,"identity":"a58f8676-95e6-40f7-b4c8-a732e84ae096","order_by":5,"name":"Yining Zhang","email":"","orcid":"","institution":"Lanzhou University","correspondingAuthor":false,"prefix":"","firstName":"Yining","middleName":"","lastName":"Zhang","suffix":""}],"badges":[],"createdAt":"2025-01-12 12:23:07","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5813558/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5813558/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s12520-025-02247-x","type":"published","date":"2025-06-13T15:57:11+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":81605498,"identity":"bd7435c5-14ed-490f-8820-cb4838178a80","added_by":"auto","created_at":"2025-04-29 05:41:02","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":680823,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSpatial distribution of different construction techniques\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-5813558/v1/5a38d5ada6760c95e604a342.png"},{"id":81605497,"identity":"ca8b7fa3-7ae6-4b44-8395-6985178a6264","added_by":"auto","created_at":"2025-04-29 05:41:02","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1321323,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eConstruction technology photos: (a) Adobe (Yanchi fire beacon tower); (b) Mix soil-rock structure (Subhash Buddhist Temple); (c) Cob (Jiaohe Ancient City); (d) Wattle and daub (Fujian Tulou); (e) Stacked earth (Xiagu City); (f) Rammed earth (Suoyang Ancient City); (g) Cut left (Jiaohe Ancient City); (h) Grass-wrapped mud (Liangzhu Cultural Relics)\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-5813558/v1/1d88050fd75178ce8f57bf20.png"},{"id":81606716,"identity":"97315c26-bed2-463e-ad8d-8002d1088373","added_by":"auto","created_at":"2025-04-29 06:05:10","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":146742,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eDistribution of construction technologies in different historical periods: (a) Embryonic stage; (b) Developmental stage; (c) Forming stage; (d) Application stage; (e) Transition stage\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-5813558/v1/2bb99257c9cb2d8a3e129272.png"},{"id":81605501,"identity":"596025cf-65db-4de6-9b93-7064a98833b2","added_by":"auto","created_at":"2025-04-29 05:41:03","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":1155862,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eKDE of different construction techniques: (a) Rammed earth; (b)Stacked earth; (c) Cut left; (d) Grass-wrapped mud; (e) Wattle and daub; (f) Adobe\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-5813558/v1/ebf4d2be29e8a890083adf72.png"},{"id":81605515,"identity":"58e18440-e729-436e-81d9-585882174940","added_by":"auto","created_at":"2025-04-29 05:41:04","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":569249,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eTriangular coordinate map of soil texture classification: (a) Adobe; (b) Mix soil-rock structure; (c) Cob; (d) Wattle and daub; (e) Stacked earth; (f) Rammed earth; (g) Cut left; (h) Grass-wrapped mud\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-5813558/v1/9a8a6efc680dfebeda829c7c.png"},{"id":81605508,"identity":"c77fe5fb-3234-4673-8fb1-8364882f3dc0","added_by":"auto","created_at":"2025-04-29 05:41:03","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":662140,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ePercentage of sites in different climatic zones\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-5813558/v1/288f6a27e6e3fe09d4ff2b9a.png"},{"id":81605505,"identity":"2c5c533c-a78c-406c-8006-a79e52e6aea5","added_by":"auto","created_at":"2025-04-29 05:41:03","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":719242,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eGeomorphological map for construction technology\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-5813558/v1/70f0794b10cb2b93fcfd4209.png"},{"id":81605503,"identity":"952c4df4-78c3-41cc-a08e-5ba67f7f8ee1","added_by":"auto","created_at":"2025-04-29 05:41:03","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":906373,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eKDE and Directional Distribution of construction technologies over time: (a) Neolithic; (b) Xia, Shang and Zhou dynasties; (c) Qin and Han dynasties; (d) Tang and Song dynasties; (e) Yuan, Ming and Qing dynasties\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-5813558/v1/ad0a48bd666a78a4f84edefa.png"},{"id":81605519,"identity":"31a334bf-f59a-4b82-9c3f-c8881660c2a1","added_by":"auto","created_at":"2025-04-29 05:41:04","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":652888,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eMap of ellipse center migration for different periods\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-5813558/v1/31be145a956db4ebf0a919cd.png"},{"id":84726475,"identity":"f7e829b3-30aa-4bfe-86f4-c9adc929a032","added_by":"auto","created_at":"2025-06-16 16:05:27","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":8348026,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5813558/v1/27b7702a-32c4-4e9b-b8d3-7e3a98e1ec14.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Characterization of spatial and temporal evolution of earthen sites construction technology in China based on GIS","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eEarth, as a fundamental building material, has played a pivotal role in the evolution of ancient architecture[1, 2]. \u0026quot;Earthen sites\u0026quot; is a broad term referring to the material remains of historical, artistic, scientific, social, and cultural value created by humans or associated with human activities, in which earth is the primary building material, and which have been preserved throughout human historical development[3, 4]. The construction of earthen sites has been influenced by various factors, such as the productivity levels of the era, the environmental conditions, and the functional needs, which together resulted in the development of distinct construction techniques[5-7]. Ivo Herle[8] provides a comprehensive examination of the development of raw earth construction internationally, while P. Doat and Gernot Minke detail a variety of earth construction techniques through an in-depth study of raw earth construction and its global literature[9]. John Norton further integrates modern concepts of raw earth architecture and analyzes the advancement of raw earth building techniques at a theoretical level[10]. The International Center for Raw Earth Architecture (CRATerre-ENSAG) in France has classified raw earth construction methods worldwide into twelve material-processing techniques, such as rammed earth, masonry, extrusion, molding, plastering, pressing, cutting, covering, and filling, as well as eighteen types of raw earth applications, including adobe, rammed earth, pressed earth bricks, straw mudballs, and wattle and daub[11]. In addition, \u003cem\u003eThe Guides de bonnes pratiques de la construction en terre crue\u003c/em\u003e, for the guidance of the restoration of new and old buildings, categorizes the techniques of raw earth into: les torchis, les briques de terre crue, le pies, la bauge, la terre all\u0026eacute;g\u0026eacute;e, les enduits en terre[12]. German archaeologists have created a vocabulary of the \u0026ldquo;cob balls, adobe, and daubed straw plaits\u0026rdquo; technique in four languages by investigating earthen architecture in Europe and Central Asia[13]. Some scholars have also systematically analyzed the technology of raw earth as a load-bearing body and wall covering[14]. The above study provides us with a basis for distinguishing between earthen buildings, archaeological sites and heritage buildings in our field survey. Therefore, it should be emphasized that the earth sites involved in this study refer to open-air building bodies with earth as the main building material and earth as load-bearing material, which have historical and cultural values. \u003c/p\u003e\n\u003cp\u003eDue to its long history and vast geographical expanse, China is distinguished by a large number of earthen sites and a rich diversity of construction techniques[15]. Chinese archaeological and documentary data show that in the Paleolithic Age about 100,000 years ago, ancient humans dug caves and lived in them, and at this time, the main construction technology was digging and building in the raw earth. By the Neolithic Age (10,000 years ago - 5,000 years ago), the gradual emergence of ground construction, stacks of mud method wood and bone mud walls, and other technologies were applied by the ancients[16]. About 4,000 years ago, at the Longshan cultural site, the emergence of rammed earth construction for city walls, foundations, and other structures occurred[17, 18]. With the development of social productivity and the increase in demand, a wide variety of construction techniques based on rammed earth and adobe appeared in different regions and at different times across China. Techniques for constructing earthen sites have been well-documented in ancient China. Among these, the Song Dynasty (960 A.D.) in its \u0026quot;Methods of Construction\u0026quot; quantified the methods used in Chinese earthen buildings, leading to the establishment of specific architectural norms[19]. The \u0026quot;Standards of Architectural Engineering\u0026quot; from the Qing Dynasty (1616 A.D.) outlined operational procedures for earthen construction techniques[20]. Since the 21st century, Zhang has categorized Chinese earthwork construction methods into five types: cut left, rammed earth, cob, adobe, and earth block construction[17]; Pei classified earthen architectural construction techniques into five major categories and fifteen subcategories: cut left, stacked earth, rammed earth, adobe, and cob[21]. Based on a review of the literature and field investigations, this study categorizes earthen site construction techniques into eight types: cut left, stacked earth, rammed earth, cob, adobe, wattle and daub, mixed earth-rock structure, and grass-wrapped mud.\u003c/p\u003e\n\u003cp\u003eIn terms of the spatial and temporal evolution of construction technology, Pei[21], Xue[22], and Li[23] have conducted relevant studies on the Great Wall construction techniques, the evolution of earth-building methods, and the development and application of raw earth construction technologies, respectively. However, these studies were conducted regionally and have not addressed the issue on a national scale. Given that Chinese earthen sites span a long period, a large number of sites, and a vast geographical area, it is extremely challenging to analyze their construction techniques both temporally and spatially. Geographic Information Systems (GIS) offer a solution to these challenges due to their powerful ability to manage and analyze spatial data. Li [24] employed spatial analysis methods, such as Kernel Density Estimation (KDE) and trend surface analysis, to examine the spatial and temporal distribution of ancient Chinese archaeological sites and the factors influencing them. Li [25] explored the relationship between the spatial and temporal distribution of grottoes and the natural environment in Henan Province, China, using GIS for processing and visualization. Using GIS KDE, Du examined how population density affected the Ming Great Wall in Qinghai, China[26]. Chen et al. employed the GIS-FAHP method to map the freeze-thaw sensitivity of soil sites in China, considering the intensity of freeze-thaw conditions and the natural landscape variations [27]. These studies have demonstrated the strong performance of GIS in spatial analysis. However, current analyses of the evolution of construction techniques primarily involve literature reviews and generalizations, lacking visualization and quantitative analysis. Therefore, this study will utilize GIS to visualize and quantify the spatial and temporal evolution of construction techniques for Chinese earthen sites.\u003c/p\u003e\n\u003cp\u003eThis study compiles the construction histories and techniques of 553 state-protected earthen sites with well-documented construction methods. Through a review of the literature, these sites are categorized according to their historical periods. The spatial and temporal distribution, as well as the evolutionary characteristics of construction techniques, are then analyzed using KDE, the Center of Gravity Migration model, and Standard Deviation Ellipse (SDE) in GIS spatial analysis methods. Finally, the influencing factors behind the spatial distribution of construction techniques and the mechanisms governing their spatial and temporal evolution are explored. In essence, the temporal and spatial evolution of earthen site construction techniques results from the combined effects of geological environmental conditions and human social factors. Consequently, studying these techniques helps reveal the interconnected, interdependent, and interpenetrating relationship between humanity and nature, and is of significant engineering and historical importance.\u003c/p\u003e"},{"header":"2. Materials and Methods","content":"\u003cp\u003e\u003cstrong\u003e2.1 Study area\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eChina, with its rich historical legacy and vast geographical expanse, is home to numerous earthen sites, which are distinguished by their long history, large number, extensive geographical distribution, significant cultural value, and diverse construction techniques. Thus, China has been selected as the focus of this study. According to data released by the State Administration of Cultural Heritage of China, there are 875 earthen sites included in the national key cultural relics protection list. Of these, 553 earthen sites have documented construction techniques and their respective construction periods. This study thus focuses on these 553 sites to examine the temporal and spatial evolution of construction techniques employed in Chinese earthen sites.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e2.1.1\u003c/strong\u003e \u003cstrong\u003eTypes of construction techniques\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThrough the collection and analysis of historical data on the construction techniques of earthen sites, these techniques can be categorized into eight distinct types: cut left, stacked earth, rammed earth, cob, adobe, wattle and daub, mixed earth-rock structure, and grass-wrapped mud. Fig. 1 illustrates the spatial distribution of the various construction techniques employed at the earthen sites. The specific data on the construction techniques and periods of the 553 sites are shown in Table 1. It should be noted that due to the lack of precise information on the generation breaks of some of the sites (it is only possible to determine the dynasty to which they belong). In order to ensure the scientific and comparable nature of the research data, this study uses the dynasty as the basic statistical unit.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 1: Sites construction techniques and periods\u003c/strong\u003e\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"100%\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 21.875%;\"\u003e\n \u003cp\u003ePeriods/Techniques\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 9.375%;\"\u003e\n \u003cp\u003eAdobe\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 12.5%;\"\u003e\n \u003cp\u003eMix soil-rock structure\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6.25%;\"\u003e\n \u003cp\u003eCob\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 9.375%;\"\u003e\n \u003cp\u003eWattle and daub\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10.4167%;\"\u003e\n \u003cp\u003eStacked earth\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 11.4583%;\"\u003e\n \u003cp\u003eRammed earth\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6.25%;\"\u003e\n \u003cp\u003eCut left\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 12.5%;\"\u003e\n \u003cp\u003eGrass-wrapped mud\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 21.875%;\"\u003e\n \u003cp\u003ePrehistory (Before 2070 B.C.)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 9.375%;\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 12.5%;\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6.25%;\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 9.375%;\"\u003e\n \u003cp\u003e12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10.4167%;\"\u003e\n \u003cp\u003e26\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 11.4583%;\"\u003e\n \u003cp\u003e22\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6.25%;\"\u003e\n \u003cp\u003e54\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 12.5%;\"\u003e\n \u003cp\u003e9\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 21.875%;\"\u003e\n \u003cp\u003eXia, Shang and Zhou (2070 B.C. - 221 B.C.)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 9.375%;\"\u003e\n \u003cp\u003e6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 12.5%;\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6.25%;\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 9.375%;\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10.4167%;\"\u003e\n \u003cp\u003e10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 11.4583%;\"\u003e\n \u003cp\u003e97\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6.25%;\"\u003e\n \u003cp\u003e6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 12.5%;\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 21.875%;\"\u003e\n \u003cp\u003eQin and Han（including Wei and Jin） (221 B.C. - 618 A.D.)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 9.375%;\"\u003e\n \u003cp\u003e12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 12.5%;\"\u003e\n \u003cp\u003e6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6.25%;\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 9.375%;\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10.4167%;\"\u003e\n \u003cp\u003e7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 11.4583%;\"\u003e\n \u003cp\u003e107\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6.25%;\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 12.5%;\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 21.875%;\"\u003e\n \u003cp\u003eTang and Song (618 A.D. - 1206 A.D.)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 9.375%;\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 12.5%;\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6.25%;\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 9.375%;\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10.4167%;\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 11.4583%;\"\u003e\n \u003cp\u003e107\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6.25%;\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 12.5%;\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 21.875%;\"\u003e\n \u003cp\u003eYuan, Ming and Qing (1206 A.D. - 1911 A.D.)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 9.375%;\"\u003e\n \u003cp\u003e9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 12.5%;\"\u003e\n \u003cp\u003e7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6.25%;\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 9.375%;\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10.4167%;\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 11.4583%;\"\u003e\n \u003cp\u003e30\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6.25%;\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 12.5%;\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eThe authors have divided the construction techniques of earthen sites into pure earth techniques (rammed earth, stacked earth, cut left), mixed techniques (cob, grass-wrapped mud, wattle and daub, mixed soil-rock structures), and prefabricated technique (adobe). The reason for the separate distinction between adobe is that it differs significantly from the other technologies in sociological and anthropological terms. Specifically, the manufactured adobe is capable of being used by different people in different places. The technological characteristics of each technique are described below:\u003c/p\u003e\n\u003cp\u003e(1) Adobe\u003c/p\u003e\n\u003cp\u003eAdobe (Fig. 2a) is a technique in which blocks of the desired shape are made from loose soil through specific processing methods and then assembled into structures. The typical processing method for adobe involves mixing water with soil to create mud, reshaping the mud into blocks, drying them in the sun, and finally using the dried adobe blocks for masonry. Adobe masonry is generally divided into two main categories: The first involves shaping the blocks by hand according to the requirements of the structure or use, without the use of molds. The second category involves mixing the soil, placing it into a mold, pressing it into shape, and then drying it for use in masonry. In some regions, straw is added to the adobe bricks to increase their tensile strength. \u003c/p\u003e\n\u003cp\u003e(2) Mixed earth-rock structure\u003c/p\u003e\n\u003cp\u003eThe mixed earth-rock structure (Fig. 2b) primarily involves the incorporation of stones or rocks into earthen ramparts or fortifications. Another important form of this construction technique is the use of clad brick walls as part of the earth-and-stone hybrid structure (A complete earthen structure (rammed earth, adobe) with an external layer of masonry on the inside). The key feature of this technique is the addition of stones or pebbles to the earth, which improves the structural integrity. Additionally, in some methods, alternating layers of earth and stone or large pebbles are used as a foundation base, which helps reduce the settlement of the earth by distributing the load more evenly.\u003c/p\u003e\n\u003cp\u003e(3) Cob\u003c/p\u003e\n\u003cp\u003eThe primary materials for cob construction (Fig. 2c) are sand, water, and mortar, with straw and stalks often added to enhance the mixture. These materials are mixed and stacked to form walls. The specific method is to control the shape of the cob by hand; no other tools are used, and the surface is repaired after the main body of the cob is completed. It is important to emphasize that the shape of the cob is blocky so that cracks between the different cob blocks will be evident after drying.\u003c/p\u003e\n\u003cp\u003e(4) Wattle and daub\u003c/p\u003e\n\u003cp\u003eThe wattle and daub method (Fig. 2d) involves using a wooden or bamboo frame as the skeleton, which is then woven and tied to form a three-dimensional mesh. Gaps in the structure are filled with a mud-and-grass mixture, enhancing the overall stability of the wall. This construction method also improves the thermal insulation and heat resistance properties of the building compared to traditional crypt-type housing. \u003c/p\u003e\n\u003cp\u003e(5) Stacked earth\u003c/p\u003e\n\u003cp\u003eStacked earth (Fig. 2e) is commonly found in early earthen sites in southern China. In this region, due to the high clay and water content of the soil, direct ramming is not feasible. Preparation of the building can be accomplished by layering the soil along the height. There is no tamping process in this technique.\u003c/p\u003e\n\u003cp\u003e(6) Rammed earth\u003c/p\u003e\n\u003cp\u003eRammed earth (Fig. 2f) involves compacting soil with specialized tools to increase its density and firmness, creating a solid structure through the application of external force. Rammed earth is one of the most widely used construction techniques in China\u0026apos;s raw earth architecture. This technique can be further divided into two types: direct rammed earth and plate-rammed earth, depending on the specific construction method employed. Visible tamped layers and tamped nests are the key discriminatory criteria for identifying this technique.\u003c/p\u003e\n\u003cp\u003e(7) Cut left\u003c/p\u003e\n\u003cp\u003eCut left (Fig. 2g) refers to a technique in which the exposed portion of the earth is excavated and used as the primary building material. The process generally involves first determining the building\u0026apos;s layout and location, then excavating the surrounding soil, leaving the remaining earth in place to form the walls. This technique is used to create buildings such as houses and roads by utilizing the natural earth around them.\u003c/p\u003e\n\u003cp\u003e(8) Grass-wrapped mud\u003c/p\u003e\n\u003cp\u003eGrass-wrapped mud (Fig. 2h) is a construction technique used in wet environments, where a block of thatch or rushes is wrapped around soil and secured with plant fibers. This method is often found in primitive human dwellings. Its main advantages include high mobility, cost-effectiveness, easy availability of materials, and excellent thermal insulation properties.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e2.2 Methods\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e2.2.1 Method of Dividing Construction Technology Stages\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003ePeriodic classification is a method of categorizing artifacts according to the era in which they were produced. Each artifact can be traced back to a specific period, allowing for the classification of artifacts by their respective eras. By collecting and categorizing artifacts from the same period, it becomes easier to study the differences and developments between artifacts from various timeframes. Based on the chronological classification of artifacts from earthen sites, construction techniques are categorized according to the corresponding periods. Initially, data on the construction dates and techniques of state-protected earthen sites are collected. Subsequently, using the framework provided in the \u003cem\u003eHistory of Ancient Chinese Architecture\u003c/em\u003e[28], the construction technologies of Chinese earthen sites are divided into distinct stages based on historical periods.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e2.2.2 Methodology for characterization of spatial and temporal evolution\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll spatial analyses in this study were conducted exclusively using ArcGIS Pro 3.0. The China Geodetic Coordinate System 2000 (CGCS2000) was adopted as the geographic coordinate system, while the Gauss-Kr\u0026uuml;ger projection served as the projected coordinate system. Statistics and plotting were performed using Excel 2021 and Origin 2025 software, respectively. The principles and formulas of the Kernel Density Estimation (KDE) and Standard Deviation Ellipse (SDE) method used in this study are all referred to in the help manual (ArcGIS Pro help\u0026mdash;ArcGIS Pro | Documentation) and \u003cem\u003eThe ESRI guide to GIS analysis\u003c/em\u003e in ArcGIS Pro[29].\u003c/p\u003e\n\u003cp\u003e(1) Kernel Density Estimation\u003c/p\u003e\n\u003cp\u003eKernel Density Estimation (KDE) is a nonparametric statistical method that generates a continuous density surface by spreading the density contribution of each point to the surrounding area[30]. The core idea is to calculate the density contribution of each point to the surrounding area through the kernel function and determine the range of density diffusion through the search radius. In the field of cultural heritage, KDE is mainly used to reflect the degree of aggregation of sites[24]. Therefore, in this study, this method is used to analyze the spatiotemporal distribution characteristics of earthen site construction technology.\u003c/p\u003e\n\u003cp\u003eThe search radius directly affects the results of KDE. A radius that is too large or too small will lead to deviations in the results. In this study, the default search radius was used. The algorithm used to determine the default search radius (also known as the bandwidth) will perform the following operations: calculate the mean center of the input points; calculate the distances of all points to the mean center; calculate the median of these distances; calculate the standard distance. Then, the calculation is performed using the corresponding formula. For detailed procedures, see the ArcGIS Pro Help Manual. This method for selecting the search radius is based on the \u0026quot;Silverman Rule of Experience\u0026quot; bandwidth estimation formula. This method of calculating the default radius usually avoids the ring phenomenon around points that often appear in sparse data sets and prevents spatial outliers - that is, several points far away from the rest of the points[30]. Since the number and distribution range of the ruins sites in different periods are inconsistent, the calculated default radius is also different. If the radius is different, the absolute magnitude of the density value cannot be directly compared, but the spatial distribution pattern may still have reference value. If a unified search radius is used, it can ensure the comparability of the absolute density value, but it will result in over-smoothing of sparse data sets or under-smoothing of dense data sets. The above two cannot be satisfied at the same time. Therefore, in this study, the author adopts the method of unified search radius. Specifically, first, calculate the default search radius of each building technology separately and select the maximum recommended radius as the unified value. The calculation results show that the search radius of the wooden frame mud wall is the largest, which is 715534.855 m, which is the search radius of this study. In addition, the search range and output pixel are unified. The search range is the Chinese area, and the output pixel size is 9000\u0026times;9000. For the five periods, the same method was adopted to determine a unified search radius for the kernel density estimation. Through calculation, the unified search radius was determined as 446543.454 m, while all other parameters remained consistent with the previous settings.\u003c/p\u003e\n\u003cp\u003e(2) Directional Distribution (Standard Deviational Ellipses)\u003c/p\u003e\n\u003cp\u003eA common method for measuring the trend for a set of points or areas is to calculate standard distances in the x, y, and z directions. These measurements can be used to define the axes of an ellipse (or ellipsoid) that encompasses the distribution of all features. Because the axes of the ellipse are defined by calculating the standard deviations of the x and y coordinates about the mean center, the ellipse is called a Standard Deviational Ellipse (SDE)[29]. This method is widely used to analyze the distribution and characteristic changes of geographical spatial elements[31, 32]. This study uses this method to analyze the distribution direction, dispersion degree, and central trend of different building technologies.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e2.2.3 Methods of analyzing the factors influencing construction technology\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eEarth site construction techniques are closely related to the environment (including climate, soil texture and topography) of the region in which they are located. Therefore, in this study, the vector dataset of annual average precipitation, soil texture and topography at the scale of 1:1,000,000 was obtained from the Resource Environment and Data Center of the Chinese Academy of Sciences (\u003cu\u003ehttps://www.resdc.cn/\u003c/u\u003e). The above data were analyzed by Overlay Analysis with site point data; precipitation, soil texture and geomorphology type attributes were accurately associated to each site point by using the Extract Multi Values to Points tool in ArcGIS Pro; and statistical analyses were subsequently performed to study the characteristics of the environmental elements of the different construction techniques. It should be noted that for the soil texture data, according to the classification criteria of the United States Department of Agriculture (USDA)[33], based on the difference in the proportion of content of the three grain groups of sand (2-0.05 mm), silt (0.05 - 0.002 mm), and clay (\u0026lt;0.002 mm), the soils were categorized as follows: Sand, Loamy Sand, Sandy Clay, Sandy Clay Loam. Sandy Loam, Clay Loam, Loam, Silty Loam, Silt, Silty Clay Loam, Silty Clay, Clay. Finally, the differences in soil texture between construction techniques were statistically analyzed.\u003c/p\u003e"},{"header":"3. Results","content":"\u003cp\u003e\u003cstrong\u003e3.1 Stages of Construction Technology\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eIn this study, we first compiled the construction technologies and dynasties of construction for 553 earthen sites. Based on the historical development of ancient Chinese society, cultural exchanges, and advancements in construction technology, the evolution of earthen site construction can be divided into five stages: the embryonic stage, the development stage, the forming stage, the application stage, and the transition stage. The main characteristics of each stage are described in Table 2.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.1.1 Embryonic stage\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe prehistoric period in China is classified as the embryonic stage of earthen site construction technology. Spanning from approximately before 2070 B.C., this period marks the transition of human habitation from caves to above-ground structures. The specific reference comes from the \u003cem\u003eDictionary of Chinese Archaeology\u003c/em\u003e[34].\u003c/p\u003e\n\u003cp\u003eThe distribution of construction techniques during this period reflects the productivity levels and human needs of the time, as shown in Fig. 3a. The dominant construction methods were \u003cem\u003ecut left\u003c/em\u003e (41.50%), followed by rammed earth (16.90%) and stacked earth (20%). The construction techniques of stacked earth and cut left were widely used in earthen sites in the early primitive period because they were relatively simple and required relatively low labor levels. For example, the Pengtoushan culture in the Yangtze River Basin (7500 B.C. to 6100 B.C.) had already seen the use of stacked earth and cut left[35]. During the same period, underground or semi-underground buildings were also discovered at the Jiahu cultural site in the upper reaches of the Huaihe River[36]. In the middle Neolithic period, at the Xinglongwa cultural site in northern China (6300 B.C.-5400 B.C.), the use of grass-wrapped mud appeared[37]. Three houses were discovered at the Dawenkou site in the lower reaches of the Yellow River in my country (4400 B.C.-2600 B.C.), which were built using the cob[38]. The earliest architectural site discovered so far that used wattle and daub construction technology should be the Miaodigou site in the middle period of the Yangshao culture (3900 B.C.-3600 B.C.). During the same period, the Zhengzhou Xishan site in the late Yangshao culture (3900 B.C.-2900 B.C.) showed the technology of rammed earth[39]. The earliest adobe construction technology discovered in my country is the Menbanwan site of the Qujialing culture (3300 B.C. to 2500 B.C.)[40]. The mixed earth-rock structure was used more in the early sites in mountainous areas. The technology appeared in the stone piles of the Miaodigou II culture (3400 B.C.-3100 B.C.)[41]. These technological advances not only reflect human adaptation to the environment but also signal progress in building techniques and social structures.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.1.2 Developmental stage\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eDuring the Xia, Shang, and Zhou dynasties (2070 B.C. - 221 B.C.), societal shifts from clan-based communal ownership to private family ownership resulted in heightened social differentiation and the formation of hierarchies. This period witnessed significant advancements in earthen site construction techniques, closely linked to improved productivity and the expansion of human needs. The construction of city walls for defense and the rise of high-platform buildings- often with rammed earth foundations- served both practical and symbolic functions, representing social status and ritual significance. As seen in Fig. 3b, the use of \u003cem\u003ecut left\u003c/em\u003e and stacked earth methods decreased to 5% and 8%, respectively, as these techniques could no longer meet the growing demands for strength and durability. Conversely, the proportion of rammed earth constructions increased significantly to 78.9%, reflecting the evolution of social structures and the advancement of construction technologies.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.1.3 Forming stage\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe Qin-Han period (including the Wei and Jin dynasties) (221 B.C. - 618 A.D.) saw the establishment of a centralized power system as society transitioned from slavery to feudalism[42]. This period marked significant developments in earthen site construction, fueled by increased productivity and growing human needs. Construction techniques became more refined, particularly with the advent of preparation techniques and the rammed-earth plate construction method. Advances in materials such as bamboo, grass, reeds, and hemp ropes played a crucial role in enhancing rammed earth technology. City walls were built not only for defense but also to symbolize ritual status and power, often elevated on rammed earth foundations[43]. Similarly, the palace buildings of the ruling class began to adopt a combination of rammed earth, adobe, and timber-framed techniques to achieve both aesthetic and functional effects. During this period, 78.7% of earthen sites employed rammed earth, while the use of adobe increased to 8.9%. In contrast, the use of \u003cem\u003ecut left\u003c/em\u003e and wattle and daub techniques declined to 2% (Fig. 3c). The earthen site construction process began to take its current form, with rammed earth becoming the dominant technique.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.1.4 Application stage\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eDuring the Tang and Song dynasties (618 A.D. - 1206 A.D.), the use of rammed earth construction techniques further increased, accounting for 91.5% of the total. Conversely, the use of stacked earth, wattle and daub, and grass-wrapped mud techniques declined, with stacked earth representing only 1% (Fig. 3d). This period saw minimal use of \u003cem\u003ecut left\u003c/em\u003e techniques, while adobe construction became more widespread, often in combination with rammed earth. This shift reflects the diversification and advancement of earthen site construction techniques.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.1.5 Transition stage\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eBy the Yuan, Ming, and Qing dynasties (1206 A.D. - 1911 A.D.), brick and wood structures became the dominant construction methods[44]. During the Yuan Dynasty, wooden structures were simplified and became a significant architectural form in China. The development of brick-making technology and lime-based bonding materials led to the widespread use of masonry techniques in palaces, temples, and other buildings. Although the number of earthen sites decreased during this period, earthen construction techniques continued to be used, though in more refined forms. A typical example is the Ming Great Wall, which still stands today. During this period, earth tamping remained the primary technique (Fig. 3e), but the overall number of state-protected earthen sites declined, reflecting the broader trend of transitioning from earthen to wood and masonry construction techniques.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 2: E\u003c/strong\u003e\u003cstrong\u003earthen heritage sites process stages\u003c/strong\u003e\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"100%\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 20.4082%;\"\u003e\n \u003cp\u003eConstruction techniques\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 13.2653%;\"\u003e\n \u003cp\u003eperiods\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 66.3265%;\"\u003e\n \u003cp\u003eCharacteristics of the periods\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 20.4082%;\"\u003e\n \u003cp\u003eEmbryonic stage (Before 2070 B.C.)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 13.2653%;\"\u003e\n \u003cp\u003eprehistory\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 66.3265%;\"\u003e\n \u003cp\u003eA variety of construction techniques were successively produced, the process is relatively primitive and simple, with the highest proportion of cut left.\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 20.4082%;\"\u003e\n \u003cp\u003eDevelopmental stage (2070 B.C. - 221 B.C.)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 13.2653%;\"\u003e\n \u003cp\u003eXia, Shang and Zhou\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 66.3265%;\"\u003e\n \u003cp\u003eThe economic system of clan communal ownership was gradually replaced by family private ownership, the development of productivity, defensive attributes of the city wall, ritual attributes of the high platform building began to appear, and the process of rammed earth began to gradually become the mainstream process.\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 20.4082%;\"\u003e\n \u003cp\u003eForming stage (221 B.C. - 618 A.D.)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 13.2653%;\"\u003e\n \u003cp\u003eQin and Han\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 66.3265%;\"\u003e\n \u003cp\u003eThe development of the earthen site construction process took shape. The development of sophisticated hemp cordage techniques contributed to the advancement of rammed earth construction. The adobe process gradually developed from unmolded adobe to standardized molded adobe.\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 20.4082%;\"\u003e\n \u003cp\u003eApplication stage (618 A.D. - 1206 A.D.)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 13.2653%;\"\u003e\n \u003cp\u003eTang and Song\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 66.3265%;\"\u003e\n \u003cp\u003eThe combined use of various earthen site construction techniques has increased, and the construction process has gradually become scientific and rationalized.\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 20.4082%;\"\u003e\n \u003cp\u003eTransition stage (1206 A.D. - 1911 A.D.)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 13.2653%;\"\u003e\n \u003cp\u003eYuan, Ming and Qing\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 66.3265%;\"\u003e\n \u003cp\u003eThe number of earthen sites has declined, and there has been a gradual shift to masonry and wood construction for the dominant site-building techniques.\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cstrong\u003e3.2 Characterization of the spatial distribution of construction techniques at earthen sites\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.2.1 Characteristics of the overall distribution of construction technologies\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAs shown in Fig. 1, China\u0026apos;s earthen sites are mainly distributed in the Yellow River Basin and the Central Plains, the northwest arid area, the Yangtze River Basin and the southern region, and the northeast region; a small number are distributed in the Qinghai-Tibet Plateau and the southwest region. Analyzing the preservation status of the sites reveals that these technologies are concentrated mainly in the central and northern regions of China. Specifically, the \u003cem\u003ecut left\u003c/em\u003e technique is predominantly found in the middle and upper reaches of the Yellow River Basin, while \u003cem\u003estacked earth\u003c/em\u003e is mainly distributed in the middle and lower reaches of the Yangtze River, areas characterized by a humid climate and high rainfall. \u003cem\u003eAdobe\u003c/em\u003e is widely used in Xinjiang, and the core distribution of \u003cem\u003erammed earth\u003c/em\u003e extends along the Yellow River Basin. The distribution of other construction techniques is less pronounced.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.2.2 Characteristics of the distribution of different construction technologies\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eIn this study, six construction techniques (\u003cem\u003erammed earth\u003c/em\u003e, stacked earth, wattle and daub, adobe, grass-wrapped mud, and \u003cem\u003ecut left)\u0026nbsp;\u003c/em\u003ewere selected for spatial KDE. The \u003cem\u003ecob\u003c/em\u003e and \u003cem\u003emixed earth-rock\u003c/em\u003e structures were excluded from the analysis due to the limited number of site locations associated with these methods. Based on the kernel density distribution, the spatial distribution characteristics of various construction techniques are described as follows.\u003c/p\u003e\n\u003cp\u003eAs shown in Fig. 4a, as the dominant construction technique, rammed earth is widely distributed throughout the country, and its core area is located in the Central Plains, which is the center of ancient China\u0026apos;s economy and politics. Stacking earth technology is mainly distributed in the Yangtze River Basin in southern China, and a small amount appears in Northeast my country (Fig. 4b). Cut left technology is concentrated around the Yellow River Basin, and the highest distribution density is in the Loess Plateau (Fig. 4c). Grass-wrapped mud technology is mainly distributed in the Yellow River and Yangtze River Basins, and is scattered in southwest China and Xinjiang (Fig. 4d). Wattle and daub have a dual-core distribution, concentrated in the two river basins in eastern my country and southern Xinjiang (Fig. 4e). Adobe bricks are distributed in a belt along the ancient Silk Road, extending from the Hexi Corridor to western Xinjiang (Fig. 4f).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.3 Key Influencing Factors of Earthen Heritage Construction Techniques\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eSoil texture, which refers to the relative proportions of different particle sizes in the soil, plays a critical role in determining the physical properties of the soil and significantly impacts the use of raw soil materials in construction. In this study, the U.S. soil texture classification system was used, with the content of clay (\u0026lt;0.002 mm), silt (0.002-0.05 mm), and sand (0.05-2 mm) particles represented in triangular coordinate graphs, as shown in Fig. 5.\u003c/p\u003e\n\u003cp\u003eThe results reveal that sandy clay loam was the preferred soil type for the construction techniques of adobe, mixed earth-rock structures, cob, and grass-wrapped mud. In contrast, the stacked earth technique tends to favor clay loam soils. Soils with moderate amounts of clay and sand, such as sandy loam and clay loam, are typically used for techniques such as cut left, wattle and daub, and rammed earth. In particular, the rammed earth technique is used in an area with a wide range of soil types.\u003c/p\u003e"},{"header":"4. Discussion","content":"\u003cp\u003eNumerous studies have demonstrated that the spatial and temporal evolution of construction techniques at earthen sites is closely linked to natural, human, and technological factors[45]. Natural elements, such as climate, soil quality, and topography, form the geographical conditions that influence the application of construction techniques. Human elements, including production activities, social structure, and cultural customs, serve as the driving forces behind the demand for these technologies. Technological elements, such as the economic and technical capabilities of the builders, set the conditions under which these construction techniques develop.\u003c/p\u003e\n\u003cp\u003eIn the early stages of applying raw soil construction techniques, people underwent a trial-and-error process, adapting to local natural conditions to find the most suitable building methods that would meet production and living needs. Once a particular architectural form, technical system, or construction process gained general acceptance in a region, it was widely replicated. As economic and technological capabilities improved, people\u0026rsquo;s evolving material and spiritual needs led to further advancements and refinements in existing techniques, systems, and processes, often driving innovation[46].\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e4.1 Factors influencing the spatial distribution of construction technologies\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNatural factors, which form the basis of construction technologies, significantly influence the spatial distribution of these techniques. To explore this, this study analyzes the impact of climate, soil quality, and topography in the areas where the selected earthen sites are located, using statistical data.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e4.1.1 Climatic factor\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eClimatic differences, particularly variations in rainfall, have had a profound impact on the development of construction techniques at earthen sites. China can be divided into several climatic zones based on annual precipitation: arid (\u0026lt;200 mm), semi-arid (200-400 mm), semi-humid (400-800 mm), humid (800-1200 mm), and wet (\u0026gt;1200 mm) (Fig. 6). Statistically, the proportion of \u003cem\u003eadobe\u003c/em\u003e construction is highest in the arid zone at 81 %, while \u003cem\u003estacked earth\u003c/em\u003e is predominantly found in humid and wet zones, accounting for about 82 % in these regions. Other technologies are predominantly found in semi-humid zones (Table 3).\u003c/p\u003e\n\u003cp\u003eClimatic conditions have influenced the creation of these construction techniques from the outset[47]. The origins of construction methods differ between the Yellow River Basin and the Yangtze River Basin. In the Yangtze River Basin, characterized by low-lying terrain, a hot and humid climate, and a dense water network, nest dwellings developed in lake and swamp areas. These regions, rich in water and natural resources, were ideal for early human settlements based on fishing, hunting, and gathering[48]. In this environment, elevated dwellings made from wooden materials emerged, as the region lacked natural caves. Conversely, the Yellow River Basin, with its dry climate and loess-rich soil, saw the development of cave dwellings-specifically loess cave dwellings- which were more suitable to the area\u0026apos;s low rainfall[49].\u003c/p\u003e\n\u003cp\u003eIn the arid region of Xinjiang, characterized by very low annual precipitation, the \u003cem\u003ecut left\u003c/em\u003e construction technique was developed. The region\u0026apos;s low rainfall meant that rainwater erosion had minimal impact on the exposed parts of the earth, allowing buildings constructed with this technique to be better preserved over time.\u003c/p\u003e\n\u003cp\u003eWith the passage of time, the \u003cem\u003erammed earth\u003c/em\u003e construction technique gradually became the primary method for building earthen structures, spreading throughout China. However, there are regional variations in \u003cem\u003erammed earth\u003c/em\u003e technology. In northern regions, where the primary need is for heat preservation and protection against cold winters, \u003cem\u003erammed earth\u003c/em\u003e walls are thicker. This method typically involves the rafter-building technique, and when the plate-building technique is used, smaller plywood sizes are employed, with internal wooden pillars supporting the walls. In contrast, in southern regions, where moisture protection and heat resistance are more critical, \u003cem\u003erammed earth\u003c/em\u003e walls are thinner, and the plate-building method is more commonly used. Here, the plywood used is longer, and bamboo reinforcement is often added to increase wall stability, with additional efforts to seal the walls [50, 51]. These differences underscore the adaptation of building techniques to the specific climatic needs of each region.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 3:\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003ePercentage of sites in different climatic zones\u003c/strong\u003e\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"100%\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 21.875%;\"\u003e\n \u003cp\u003eZones/Techniques\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.33333%;\"\u003e\n \u003cp\u003eAdobe\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 12.5%;\"\u003e\n \u003cp\u003eMix soil-rock structure\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6.25%;\"\u003e\n \u003cp\u003eCob\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 9.375%;\"\u003e\n \u003cp\u003eWattle and daub\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10.4167%;\"\u003e\n \u003cp\u003eStacked earth\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 11.4583%;\"\u003e\n \u003cp\u003eRammed earth\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 7.29167%;\"\u003e\n \u003cp\u003eCut left\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 12.5%;\"\u003e\n \u003cp\u003eGrass-wrapped mud\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 21.875%;\"\u003e\n \u003cp\u003earid (\u0026lt;200 mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.33333%;\"\u003e\n \u003cp\u003e35 (81 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 12.5%;\"\u003e\n \u003cp\u003e3 (23 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6.25%;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 9.375%;\"\u003e\n \u003cp\u003e5 (29 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10.4167%;\"\u003e\n \u003cp\u003e1 (2 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 11.4583%;\"\u003e\n \u003cp\u003e28 (8 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 7.29167%;\"\u003e\n \u003cp\u003e2 (4 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 12.5%;\"\u003e\n \u003cp\u003e1 (8 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 21.875%;\"\u003e\n \u003cp\u003esemi-arid (200-400 mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.33333%;\"\u003e\n \u003cp\u003e2 (5 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 12.5%;\"\u003e\n \u003cp\u003e3 (23 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6.25%;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 9.375%;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10.4167%;\"\u003e\n \u003cp\u003e2 (5 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 11.4583%;\"\u003e\n \u003cp\u003e59 (16 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 7.29167%;\"\u003e\n \u003cp\u003e9 (15 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 12.5%;\"\u003e\n \u003cp\u003e1 (8 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 21.875%;\"\u003e\n \u003cp\u003esemi-humid (400-800 mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.33333%;\"\u003e\n \u003cp\u003e5 (12 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 12.5%;\"\u003e\n \u003cp\u003e6 (46 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6.25%;\"\u003e\n \u003cp\u003e1 (50 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 9.375%;\"\u003e\n \u003cp\u003e7 (41 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10.4167%;\"\u003e\n \u003cp\u003e5 (11 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 11.4583%;\"\u003e\n \u003cp\u003e216 (59 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 7.29167%;\"\u003e\n \u003cp\u003e42 (74 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 12.5%;\"\u003e\n \u003cp\u003e8 (68 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 21.875%;\"\u003e\n \u003cp\u003ehumid (800-1200 mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.33333%;\"\u003e\n \u003cp\u003e1 (2 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 12.5%;\"\u003e\n \u003cp\u003e1 (8 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6.25%;\"\u003e\n \u003cp\u003e1 (50 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 9.375%;\"\u003e\n \u003cp\u003e3 (18 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10.4167%;\"\u003e\n \u003cp\u003e19 (43 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 11.4583%;\"\u003e\n \u003cp\u003e34 (9 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 7.29167%;\"\u003e\n \u003cp\u003e3 (5 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 12.5%;\"\u003e\n \u003cp\u003e1 (8 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 21.875%;\"\u003e\n \u003cp\u003ewet (\u0026gt;1200 mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.33333%;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 12.5%;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 6.25%;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 9.375%;\"\u003e\n \u003cp\u003e2 (12 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10.4167%;\"\u003e\n \u003cp\u003e17 (39 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 11.4583%;\"\u003e\n \u003cp\u003e28 (8 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 7.29167%;\"\u003e\n \u003cp\u003e1 (2 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 12.5%;\"\u003e\n \u003cp\u003e1 (8 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cstrong\u003e4.1.2 Soil factor\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eSoil texture directly determines the feasibility, technical complexity, and preservation duration of earthen site construction techniques.\u003c/p\u003e\n\u003cp\u003eThe regional soil types corresponding to adobe construction, mixed earth-rock structures, and cob techniques predominantly consist of sandy clay loam. This particular soil composition helps minimize cracking during drying processes while enhancing structural strength[52-54]. These techniques are primarily concentrated in Northwest China where soils exhibit higher proportions of sand and silt. The stacked earth technique predominantly occurs in southern China characterized by clay loam soils. This preference arises from their elevated clay content (\u0026gt;30%) and cohesive properties that facilitate molded construction through stacking[55]. Cut left techniques are mainly distributed across the Loess Plateau with sandy loam soils, where the soil\u0026apos;s excellent integrity and moderate plasticity allow cave dwelling excavation using simple tools[56]. Both grass-wrapped mud techniques and wattle and daub constructions are associated with sandy loam and clay loam soils. These two techniques directly manifest ancient craftsmen\u0026apos;s structural innovations: the former enhances soil erosion resistance, while the latter prioritizes functional and structural stability[23].\u003c/p\u003e\n\u003cp\u003eRammed earth techniques predominantly utilize sandy loam and clay loam soils, though their application extends to diverse soil types, demonstrating exceptional geographical adaptability. Modern studies on rammed earth structures reveal that particularly sandy loam can form dense, monolithic, and structurally robust walls through compaction processes[57]. Most Chinese regions possess soil conditions suitable for rammed earth construction when appropriately modified with fine sand or other amendments, explaining its status as China\u0026apos;s most widely distributed construction technique[58]. Furthermore, rammed earth technology exemplifies ancient Chinese artisans\u0026apos; material modification expertise. Specifically, northwestern builders incorporated tamarisk branches (enhancing tensile strength) and coarse sand (reducing drying shrinkage)[22], while southern innovators utilized organic additives like glutinous rice mortar (improving cohesive strength) and egg white (forming hydrophobic membranes), enabling rammed earth applications even in humid regions with annual precipitation exceeding 800 mm[45].\u003c/p\u003e\n\u003cp\u003eThrough a tripartite adaptive mechanism of \u0026quot;local material selection \u0026ndash; performance enhancement \u0026ndash; structural innovation\u0026quot;, ancient craftsmen transformed soil limitations into technical features (e.g., loess cave dwellings, reinforced earth walls), demonstrating profound understanding and creative utilization of natural materials. This soil-property-driven technological diversity provides significant material science and engineering insights for contemporary earthen heritage conservation.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e4.1.3 Topographic factor\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTopography plays a crucial role in the development of earthen site construction techniques. Different topographic features often determine the shape of the earthen site, which in turn drives the adoption of suitable construction methods. \u003cem\u003eAccording to The Standard for 1:1,000,000 Geomorphological Mapping of China (Provisional)\u003c/em\u003e[59], China\u0026apos;s landforms can be systematically classified into seven categories based on relief amplitude: Plain (\u0026lt;20 mm), Platform (20-30 mm), Hills (30-200 mm), Low-relief Mountainous Terrain (200-500 mm), Moderate-relief Mountainous Terrain (500-1000 mm), High-relief Mountainous Terrain (1000-2500 mm), Extremely High-relief Mountainous Terrain (＞2500 mm)[60]. Relief amplitude is defined as the vertical elevation difference between a mountain ridge (summit) and either the nearest major river (with a drainage area exceeding 500 km\u0026sup2;) along the downslope direction or the closest junction point with a broader plain/platform (width \u0026gt;5 km).\u003c/p\u003e\n\u003cp\u003eIn terms of national topography, architectural techniques exhibit a clear distribution pattern influenced by the differences in terrain and geomorphology. Of the national heritage sites with detailed topographic and geomorphologic data, 553 sites were analyzed. Of these, 343 (62%) are located on plains, 113 (20%) on platforms, 52 (9%) on hills, 24 (5%) on low-relief mountainous terrain, and 21 (4%) on medium undulating mountains (Fig. 7 and Table 4). Earthen sites are predominantly concentrated in plains. This is largely because the flat and open nature of plains imposes fewer restrictions on construction techniques. In contrast, the relief mountainous terrains have a higher proportion of mixed earth-rock structures. This can be attributed to two factors: first, areas with significant terrain variation require additional materials, such as stone, to stabilize foundations; second, due to local material constraints, builders often need to select and utilize available resources based on the local environment.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 4: Percentage of sites in different landscapes\u003c/strong\u003e\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"100%\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 25.2632%;\"\u003e\n \u003cp\u003eGeomorphology (Relief Amplitude)/Techniques\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.42105%;\"\u003e\n \u003cp\u003eAdobe\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10.5263%;\"\u003e\n \u003cp\u003eMix soil-rock structure\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.42105%;\"\u003e\n \u003cp\u003eCob\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.42105%;\"\u003e\n \u003cp\u003eWattle and daub\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 9.47368%;\"\u003e\n \u003cp\u003eStacked earth\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10.5263%;\"\u003e\n \u003cp\u003eRammed earth\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.42105%;\"\u003e\n \u003cp\u003eCut left\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10.5263%;\"\u003e\n \u003cp\u003eGrass-wrapped mud\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 25.2632%;\"\u003e\n \u003cp\u003ePlain (\u0026lt;20 mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.42105%;\"\u003e\n \u003cp\u003e34 (79 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10.5263%;\"\u003e\n \u003cp\u003e9 (69 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.42105%;\"\u003e\n \u003cp\u003e1 (50 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.42105%;\"\u003e\n \u003cp\u003e13 (76 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 9.47368%;\"\u003e\n \u003cp\u003e28 (64 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10.5263%;\"\u003e\n \u003cp\u003e228 (62 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.42105%;\"\u003e\n \u003cp\u003e25 (44 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10.5263%;\"\u003e\n \u003cp\u003e5 (41 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 25.2632%;\"\u003e\n \u003cp\u003ePlatform (20-30 mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.42105%;\"\u003e\n \u003cp\u003e5 (12 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10.5263%;\"\u003e\n \u003cp\u003e1 (8 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.42105%;\"\u003e\n \u003cp\u003e1 (50 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.42105%;\"\u003e\n \u003cp\u003e2 (12 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 9.47368%;\"\u003e\n \u003cp\u003e9 (20 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10.5263%;\"\u003e\n \u003cp\u003e78 (21 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.42105%;\"\u003e\n \u003cp\u003e14 (24 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10.5263%;\"\u003e\n \u003cp\u003e3 (25 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 25.2632%;\"\u003e\n \u003cp\u003eHills (30-200 mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.42105%;\"\u003e\n \u003cp\u003e3 (7 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10.5263%;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.42105%;\"\u003e\n \u003cp\u003e\u0026nbsp;-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.42105%;\"\u003e\n \u003cp\u003e2 (12 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 9.47368%;\"\u003e\n \u003cp\u003e2 (5 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10.5263%;\"\u003e\n \u003cp\u003e31 (8 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.42105%;\"\u003e\n \u003cp\u003e12 (21 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10.5263%;\"\u003e\n \u003cp\u003e2 (17 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 25.2632%;\"\u003e\n \u003cp\u003eLow-relief Mountainous Terrain (200-500 mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.42105%;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10.5263%;\"\u003e\n \u003cp\u003e1 (8 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.42105%;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.42105%;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 9.47368%;\"\u003e\n \u003cp\u003e5 (11 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10.5263%;\"\u003e\n \u003cp\u003e16 (4 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.42105%;\"\u003e\n \u003cp\u003e2 (4 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10.5263%;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 25.2632%;\"\u003e\n \u003cp\u003eModerate-relief Mountainous Terrain (500-1000 mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.42105%;\"\u003e\n \u003cp\u003e1 (2 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10.5263%;\"\u003e\n \u003cp\u003e2 (15 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.42105%;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.42105%;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 9.47368%;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10.5263%;\"\u003e\n \u003cp\u003e12 (3 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.42105%;\"\u003e\n \u003cp\u003e4 (7 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10.5263%;\"\u003e\n \u003cp\u003e2 (17 %)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 25.2632%;\"\u003e\n \u003cp\u003eHigh-relief Mountainous Terrain (1000-2500 mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.42105%;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10.5263%;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.42105%;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.42105%;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 9.47368%;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10.5263%;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.42105%;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10.5263%;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 25.2632%;\"\u003e\n \u003cp\u003eExtremely High-relief Mountainous Terrain (＞2500 mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.42105%;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10.5263%;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.42105%;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.42105%;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 9.47368%;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10.5263%;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 8.42105%;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10.5263%;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cstrong\u003e4.2 Mechanism analysis of the spatial and temporal evolution of construction technology\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTo analyze the spatial and temporal distribution characteristics of earthen site construction techniques, this study divides the historical periods of the development of nationally protected earthen sites with different construction techniques into five time periods: the \u003cstrong\u003eprehistoric period\u0026nbsp;\u003c/strong\u003e(Before 2070 B.C.), the \u003cstrong\u003eXia, Shang, and Zhou periods\u0026nbsp;\u003c/strong\u003e(2070 B.C. - 221 B.C.), the \u003cstrong\u003eQin and Han periods\u0026nbsp;\u003c/strong\u003e(221 B.C. - 618 A.D.), the \u003cstrong\u003eTang and Song periods\u0026nbsp;\u003c/strong\u003e(618 A.D. - 1206 A.D.), and the \u003cstrong\u003eYuan, Ming, and Qing periods\u0026nbsp;\u003c/strong\u003e(1206 A.D. - 1911 A.D.). These periods correspond to the stages of development of construction techniques for earthen sites.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e4.2.1\u003c/strong\u003e\u003cstrong\u003eCharacteristics of the spatial and temporal evolution of construction technology\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eDuring the \u003cstrong\u003eprehistoric period\u003c/strong\u003e, human society had low productivity and relatively simple activities, leading to earthen site construction technology being mainly concentrated in the Yellow River and Yangtze River Basins. Specifically, the \u003cstrong\u003ecut left\u003c/strong\u003e technique was predominantly found in the middle and upper reaches of the Yellow River and the southwestern part of Northeast China. The \u003cstrong\u003estacked earth\u003c/strong\u003e technique was mainly concentrated in the central Yangtze River Basin, while \u003cstrong\u003erammed earth\u003c/strong\u003e was widely used in the middle and lower reaches of the Yellow River Basin (Fig. 8a). This period marks the area where ancient humans largely settled and is considered the cradle of Chinese civilization.\u003c/p\u003e\n\u003cp\u003eDuring the \u003cstrong\u003eXia, Shang, and Zhou periods\u003c/strong\u003e, as China transitioned from primitive society to slave society, the spatial distribution of earthen site construction techniques became more centralized, correlating closely with the scope of economic activities of the time. The \u003cstrong\u003ecut left\u003c/strong\u003e technique was drastically reduced, showing a sporadic, point-like distribution. \u003cstrong\u003eRammed earth\u003c/strong\u003e was widely spread, primarily in central Shaanxi, northwestern Shanxi, southern Hebei, and Shandong, while \u003cstrong\u003estacked earth\u003c/strong\u003e remained concentrated in the lower reaches of the Yangtze River. The latter technique was heavily influenced by the local environment and proved well-suited to the humid, rainfall-rich southern regions (Fig. 8b).\u003c/p\u003e\n\u003cp\u003eThe \u003cstrong\u003eQin-Han period\u003c/strong\u003e, which included the Wei, Jin, and Northern and Southern Dynasties, was marked by frequent warfare in Chinese history. During this period, the distribution of earthen site construction techniques became more extensive, with two core areas centered around \u003cstrong\u003eXi\u0026apos;an\u003c/strong\u003e and \u003cstrong\u003eLuoyang\u003c/strong\u003e. Additionally, a belt-shaped distribution formed along the \u003cstrong\u003eAncient Silk Road\u003c/strong\u003e, from the \u003cstrong\u003eHexi Corridor\u003c/strong\u003eto\u003cstrong\u003e\u0026nbsp;\u003cstrong\u003eXinjiang\u003c/strong\u003e\u003c/strong\u003e, reflecting the increasingly close social and cultural exchanges as Chinese civilization expanded. The distribution of construction techniques mirrored this expansion (Fig. 8c). By this time, the \u003cstrong\u003ecut left\u003c/strong\u003e technique had almost disappeared, while \u003cstrong\u003erammed earth\u003c/strong\u003e continued to be widespread. The \u003cstrong\u003eadobe\u003c/strong\u003e technique also became more common, particularly in the Xinjiang region.\u003c/p\u003e\n\u003cp\u003eBy the \u003cstrong\u003eTang and Song dynasties\u003c/strong\u003e, China experienced a period of economic prosperity and stability. Wood and masonry construction techniques had matured, partially replacing traditional earthen techniques. Nevertheless, earthen site construction technologies particularly \u003cstrong\u003erammed earth\u003c/strong\u003e, continued to be widely distributed due to their standardization and ability to integrate well with wood and masonry structures. These techniques were concentrated primarily in the middle and lower reaches of the Yellow River, northeast China, and Xinjiang (Fig. 8d).\u003c/p\u003e\n\u003cp\u003eIn the \u003cstrong\u003eYuan, Ming, and Qing dynasties\u003c/strong\u003e, the number of state-protected earthen sites declined significantly, reflecting the gradual replacement of earthen construction technologies by \u003cstrong\u003emasonry\u003c/strong\u003e and \u003cstrong\u003ewooden\u003c/strong\u003e structures. However, \u003cstrong\u003erammed earth\u003c/strong\u003e construction remained dominant, even though its geographical distribution became more dispersed (Fig. 8e). This shift in construction techniques was driven by the advancements in masonry and wood construction methods, which gradually replaced traditional earthen methods.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e4.2.2 Analysis of the directionality and center of gravity shift of construction technology in different historical periods\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eBy analyzing the \u003cstrong\u003eSDE\u003c/strong\u003e across five historical periods, we can gain insight into how the orientation and distribution of earthen site construction techniques evolved over time.\u003c/p\u003e\n\u003cp\u003eAs shown in \u003cstrong\u003eFig. 9\u003c/strong\u003e, from the \u003cstrong\u003eprehistoric period\u003c/strong\u003e to the \u003cstrong\u003eXia, Shang, and Zhou periods\u003c/strong\u003e, the azimuth of the SDE changed from 76.06\u0026deg; to 109.75\u0026deg;. In the prehistoric period, the center of gravity of earthen site construction technology was located in the northern part of \u003cstrong\u003eHenan Province\u003c/strong\u003e. This is because the region (the Yellow River Basin) is the birthplace of Chinese civilization. During the \u003cstrong\u003eXia, Shang, and Zhou periods\u003c/strong\u003e\u003cstrong\u003e,\u003c/strong\u003e this center of gravity shifted northwest along the \u003cstrong\u003eYellow River\u003c/strong\u003e by 90.18 km. The shift in the center of gravity during the Xia, Shang, and Zhou periods, on the other hand, can be attributed to the establishment of state power, which led to a reorientation of construction technology and a concentration of activity toward the north. In concrete terms, the capitals of the Xia and Shang dynasties were both located in present-day Henan Province, while the capital of the Zhou Dynasty migrated to Shaanxi Province, northwest of Henan[61]. This could plausibly explain the migration of centers and the change of direction. In addition, the distribution of earthen sites is small due to the constraints of primitive technological capabilities and the limited scope of civilization.\u003c/p\u003e\n\u003cp\u003eDuring the \u003cstrong\u003eQin and Han dynasties\u003c/strong\u003e, the center of gravity shifted significantly to the northwest by 426.59 km, and the azimuth of the SDE changed to 108.87\u0026deg;, showing a northwest-southeast orientation with greater spatial dispersion. This shift is closely linked to the rise of the \u003cstrong\u003eSilk Road\u003c/strong\u003e and the corresponding changes in political and economic centers. Cultural exchanges and nomadic pressures from the north synergistically drove the spatial expansion of earthen sites in that direction. Specifically, the opening of the Hexi Corridor and the rise of the Silk Road during the Han Dynasty are strong evidence of this[62]. By the \u003cstrong\u003eTang and Song dynasties\u003c/strong\u003e, the azimuth of the SDE was adjusted to 76.92\u0026deg;, and the spatial distribution pattern shifted to a southwest-northeast direction. The center of gravity moved northeastward by 498.53 km. The expansion of the territorial area and the reduction of conflicts on the western borders contributed to the shift in the direction of the distribution of earthen sites (northeast-southwest) and the expansion of their area. In present-day northeastern China, the Tang Dynasty fought many large-scale wars with the Gouryeo and Balhae can explain the change in the direction of distribution and the migration of direction[63].\u003c/p\u003e\n\u003cp\u003eIn the \u003cstrong\u003eYuan, Ming, and Qing dynasties\u003c/strong\u003e, the center of gravity shifted southwest by 439.33 km. The azimuth of the SDE becomes 102.58\u0026deg;. The intensification of border conflicts in the northwest and the stabilization of the eastern part of the country led to a reorientation of the distribution towards northwest-southeast. The Ming dynasty\u0026apos;s construction of nine border towns, repair of the Great Wall, and the stationing of heavy troops to deal with the nomadic forces in the northwest by strong military means are direct evidence of this[64].\u003c/p\u003e\n\u003cp\u003eThe changes not only reveal the spatial distribution characteristics of earthen site construction technology but also reflect how socio-political and economic factors influenced technological development in different historical periods.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 5: Variation of SDE parameters of\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eearth heritage sites construction technology in different historical periods\u003c/strong\u003e\u003c/p\u003e\n\u003cdiv align=\"center\"\u003e\n \u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"100%\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 17.3469%;\"\u003e\n \u003cp\u003eperiods\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 14.2857%;\"\u003e\n \u003cp\u003ecenter of gravity coordinate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 14.2857%;\"\u003e\n \u003cp\u003eL1 long axis（km）\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 14.2857%;\"\u003e\n \u003cp\u003eL2 short axis（km）\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10.2041%;\"\u003e\n \u003cp\u003eazimuth（\u0026deg;）\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 17.3469%;\"\u003e\n \u003cp\u003emigration distance（km）\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 12.2449%;\"\u003e\n \u003cp\u003edirection of migration\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 17.3469%;\"\u003e\n \u003cp\u003ePrehistoric\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 14.2857%;\"\u003e\n \u003cp\u003e112\u0026deg;21\u0026prime;42\u0026Prime;E 34\u0026deg;53\u0026prime;31\u0026Prime;N\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 14.2857%;\"\u003e\n \u003cp\u003e760.31\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 14.2857%;\"\u003e\n \u003cp\u003e592.55\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10.2041%;\"\u003e\n \u003cp\u003e76.06\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 17.3469%;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 12.2449%;\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 17.3469%;\"\u003e\n \u003cp\u003eXia, Shang and Zhou\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 14.2857%;\"\u003e\n \u003cp\u003e113\u0026deg;38\u0026prime;16\u0026Prime;E 34\u0026deg;59\u0026prime;42\u0026Prime;N\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 14.2857%;\"\u003e\n \u003cp\u003e892.71\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 14.2857%;\"\u003e\n \u003cp\u003e580.31\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10.2041%;\"\u003e\n \u003cp\u003e109.75\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 17.3469%;\"\u003e\n \u003cp\u003e90.18\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 12.2449%;\"\u003e\n \u003cp\u003enorthwest\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 17.3469%;\"\u003e\n \u003cp\u003eQin and Han\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 14.2857%;\"\u003e\n \u003cp\u003e105\u0026deg;07\u0026prime;01\u0026Prime;E 36\u0026deg;29\u0026prime;06\u0026Prime;N\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 14.2857%;\"\u003e\n \u003cp\u003e1406.11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 14.2857%;\"\u003e\n \u003cp\u003e693.82\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10.2041%;\"\u003e\n \u003cp\u003e108.87\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 17.3469%;\"\u003e\n \u003cp\u003e426.59\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 12.2449%;\"\u003e\n \u003cp\u003enorthwest\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 17.3469%;\"\u003e\n \u003cp\u003eTang and Song\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 14.2857%;\"\u003e\n \u003cp\u003e110\u0026deg;19\u0026prime;46\u0026Prime;E 39\u0026deg;44\u0026prime;09\u0026Prime;N\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 14.2857%;\"\u003e\n \u003cp\u003e1501.31\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 14.2857%;\"\u003e\n \u003cp\u003e937.57\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10.2041%;\"\u003e\n \u003cp\u003e76.92\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 17.3469%;\"\u003e\n \u003cp\u003e498.53\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 12.2449%;\"\u003e\n \u003cp\u003enortheast\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 17.3469%;\"\u003e\n \u003cp\u003eYuan, Ming and Qing\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 14.2857%;\"\u003e\n \u003cp\u003e104\u0026deg;54\u0026prime;08\u0026Prime;E 38\u0026deg;50\u0026prime;13\u0026Prime;N\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 14.2857%;\"\u003e\n \u003cp\u003e1579.36\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 14.2857%;\"\u003e\n \u003cp\u003e939.92\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 10.2041%;\"\u003e\n \u003cp\u003e102.58\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 17.3469%;\"\u003e\n \u003cp\u003e439.33\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 12.2449%;\"\u003e\n \u003cp\u003esouthwest\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e"},{"header":"5. Conclusion","content":"\u003cp\u003eBased on the data of the national key protection earth sites, this study summarizes the earth site construction techniques into eight categories based on the prior research. The development of these techniques is divided into five stages: embryonic, developmental, formative, application, and transformation. Each stage evolved in response to shifts in productivity levels and the social environment, reflecting broader societal transformations. These construction methods arise from the interaction between human ingenuity and natural conditions, embodying the collective knowledge of the workforce.\u003c/p\u003e\n\u003cp\u003e(1) In the embryonic stage, the cut left technique was predominant, accounting for 41.5% of total usage. In the developmental stage, the prevalence of cut left and stacked earth decreased, while rammed earth increased substantially to 78.9% due to its superior strength and spatial advantages. During the formative stage, rammed earth constituted 78.7% of the total, adobe increased to 8.9%, and the proportion of cut left and wattle-and-daub decreased to 2%. In the application stage, the cut left technique disappeared, and rammed earth increased to 91.5%. The use of adobe expanded, often in combination with rammed earth and other techniques, demonstrating the versatility of earthen construction methods. The transformation stage marked the decline of traditional earthen construction, with a shift toward brick and wooden structures, signaling a major technological change in construction practices.\u003c/p\u003e\n\u003cp\u003e(2) The spatial distribution of earthen architectural techniques in China exhibits regional differentiation characteristics shaped by synergistic interactions between natural and anthropogenic factors. Within the climate-soil coupling mechanism, the arid northwest region (annual precipitation \u0026lt;200 mm) demonstrates a dominance of adobe techniques (81%), facilitated by crack-resistant sandy clay loam soils containing\u0026nbsp;\u0026ge;60% sand particles. Conversely, the humid southern regions (precipitation \u0026gt;800 mm) developed stacked construction techniques (82%) through cementation processes in high-clay soils (\u0026gt;30% clay content). The semi-humid Central Plains (precipitation 400-800 mm) emerged as a concentration zone for rammed earth architecture (59%), benefiting from optimal loam textures and the geographic location of the civilizational core. Because of the simplicity of the process, its high strength, and the universality of the improved soil, the rammed earth technique is widely used throughout the country. Topographically, plains account for 69% of sites, reflecting construction advantages of flat terrain, while unique geomorphologies like loess tablelands fostered cut left techniques. This technological-geographical variation essentially represents ancient craftsmen\u0026apos;s adaptive innovations in response to regional soil-climate systems.\u003c/p\u003e\n\u003cp\u003e(3) The spatiotemporal evolution of Chinese earthen construction techniques exhibits a dynamic \u0026quot;concentration-diffusion\u0026quot; pattern, with axial shifts closely correlated to historical geopolitical transformations. During the prehistoric to Xia, Shang, and Zhou periods, constrained by primitive technical capabilities and limited civilizational boundaries, these techniques were initially developed along the Yellow and Yangtze River basins. Subsequently, the Qin-Han periods witnessed a northwest-southeast axial rotation aligned with Silk Road development, where cultural exchanges and nomadic pressures from the north synergistically drove spatial expansion along this direction. The Tang-Song period saw a strategic reorientation to a northeast-southwest distribution pattern, propelled by territorial expansion and reduced Western frontier conflicts, which facilitated both directional shifts and spatial extension. Ultimately, during the Yuan-Ming-Qing periods, intensified northwestern frontier conflicts coupled with eastern regional stabilization reconfigured the distribution axis back to a northwest-southeast orientation.\u003c/p\u003e\n\u003cp\u003eAlthough this study offers valuable insights, it is limited by the relatively small number of state-protected earthen sites, which may constrain the comprehensiveness of its findings. Future research will extend the analysis to include provincial and county-level protected earthen sites. Although GIS technology has been employed to explore the spatial, temporal, and evolutionary patterns of earthen site construction techniques, the underlying archaeological causes remain unexplored. This gap will be the focus of future investigations, as the research team plans to explore the archaeological dimensions of construction technology in greater depth.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research was supported by the National Key R\u0026amp;D Plan Program of China (Grant No. 2023YFF0905901) and Scientific and Technical Research Topics on Cultural Relics Protection in Gansu Province. Moreover, we are grateful to all the group members of this program for their assistance in the field survey and data collection.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eL. Li, M.S. Shao, S.J. Wang, Z.X. Li, Preservation of earthen heritage sites on the Silk Road, northwest China from the impact of the environment, Environmental Earth Sciences, 64 (2011) 1625-1639. https://doi.rog/10.1007/s12665-010-0829-3\u003c/li\u003e\n\u003cli\u003eF. Matero, Mud Brick Metaphysics and the Preservation of Earthen Ruins, Conservation and Management Of Archaeological Sites, 17 (2015) 209-223. https://doi.rog/10.1080/13505033.2015.1129798\u003c/li\u003e\n\u003cli\u003eA.A. Charnov, 100 Years of Site Maintenance and Repair: Conservation of Earthen Archaeological Sites in the American Southwest, Journal of Architectural Conservation, 17 (2011) 59-75. https://doi.rog/10.1080/13556207.2011.10785089\u003c/li\u003e\n\u003cli\u003eQ.L. Guo, Y.W. Wang, W.W. 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Fang, A study of the borderland administrative systems of the Yuan,the Ming and the Qing dynasties (in Chinese), Journal of Yunnan Minzu University(Philosophy and Social Sciences Edition), 33 (2016) 79-84. https://doi.rog/10.13727/j.cnki.53-1191/c.2016.01.013\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"archaeological-and-anthropological-sciences","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"aasc","sideBox":"Learn more about [Archaeological and Anthropological Sciences](http://link.springer.com/journal/12517)","snPcode":"12520","submissionUrl":"https://submission.nature.com/new-submission/12520/3","title":"Archaeological and Anthropological Sciences","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Earthen sites, Construction techniques, Distributional characteristics, Spatial and temporal evolution","lastPublishedDoi":"10.21203/rs.3.rs-5813558/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5813558/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"Chinese earthen sites are notable for their abundance, historical depth, and cultural value, with construction techniques diversifying from Prehistory to the Qing Dynasty. However, existing research has yet to provide a comprehensive quantitative analysis of the spatial and temporal evolution of construction techniques at earthen sites. This study identifies eight key techniques, including cut left, rammed earth, adobe, wattle and daub, cob, stacked earth, grass-wrapped mud, and mixed soil-rock structure. their evolution was delineated into five phases: (Ⅰ) Embryonic (Before 2070 B.C.), (Ⅱ) Development (2070 B.C.-221 B.C.), (Ⅲ) Formation (221 B.C.-618 A.D.), (Ⅳ) Application (618 A.D.-1206 A.D.), and (Ⅴ) Transformation (1206 A.D.-1911 A.D.). Spatial analysis using ArcGIS Pro tools uncovered a \"concentration-diffusion\" pattern: rammed earth techniques radiated from the Central Plains, stacked earth clustered along the Yellow and Yangtze Rivers, and cut left prevailed in early civilization regions. Quantitatively, cut left dominated the Embryonic phase (41.5%), while rammed earth usage escalated from 78.5% to 91.5% across subsequent phases, marginalizing other methods. By the Transformation phase, only four techniques persisted at 47 sites, with masonry and wood displacing earthen structures. The spatiotemporal evolution reflects dual drivers: natural factors (climate, soil, topography) and societal dynamics (productivity advances, demand shifts), epitomizing the dialectical human- environment relationship. This synthesis of technical progression and environmental adaptation not only clarifies historical construction practices but also informs contemporary strategies for heritage preservation. The findings underscore how ecological constraints and human ingenuity jointly shaped architectural innovation, offering vital insights for heritage conservation and historical research.","manuscriptTitle":"Characterization of spatial and temporal evolution of earthen sites construction technology in China based on GIS","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-04-29 05:40:57","doi":"10.21203/rs.3.rs-5813558/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-04-24T16:29:31+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-04-10T15:53:25+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-04-08T14:22:41+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"162550580693700096417804161367675072012","date":"2025-04-08T12:09:08+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"281375092214710713408603310545648315322","date":"2025-04-08T11:05:12+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-04-08T09:52:45+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-04-08T02:42:25+00:00","index":"","fulltext":""},{"type":"submitted","content":"Archaeological and Anthropological Sciences","date":"2025-04-05T08:10:29+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"archaeological-and-anthropological-sciences","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"aasc","sideBox":"Learn more about [Archaeological and Anthropological Sciences](http://link.springer.com/journal/12517)","snPcode":"12520","submissionUrl":"https://submission.nature.com/new-submission/12520/3","title":"Archaeological and Anthropological Sciences","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"67a1769f-573a-44e9-880a-f620078966a9","owner":[],"postedDate":"April 29th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-06-16T15:59:23+00:00","versionOfRecord":{"articleIdentity":"rs-5813558","link":"https://doi.org/10.1007/s12520-025-02247-x","journal":{"identity":"archaeological-and-anthropological-sciences","isVorOnly":false,"title":"Archaeological and Anthropological Sciences"},"publishedOn":"2025-06-13 15:57:11","publishedOnDateReadable":"June 13th, 2025"},"versionCreatedAt":"2025-04-29 05:40:57","video":"","vorDoi":"10.1007/s12520-025-02247-x","vorDoiUrl":"https://doi.org/10.1007/s12520-025-02247-x","workflowStages":[]},"version":"v1","identity":"rs-5813558","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5813558","identity":"rs-5813558","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}