Differential Settlement in Historic Masonry Towers: The Case of the Murcia Cathedral Bell Tower

The bell tower of Murcia Cathedral, erected between 1521 and 1793, stands as one of the most complex architectural and structural achievements of the Spanish Renaissance and Baroque. Rising 93 m above the Vega del Segura, the tower integrates successive stylistic and technical layers that reflect nearly three centuries of construction. This study analyses its architectural composition, structural configuration, and geotechnical foundation through a multidisciplinary approach combining historical documentation, non-destructive testing, and soil mechanics. Geological and geotechnical data from the Instituto Geológico y Minero de España and recent subsidence records are used to characterize the subsoil, composed of compressible silty clays with high groundwater levels and localized settlement induced by piezometric fluctuations. Structural assessment, based on Heyman’s masonry theory and Euler’s critical load criteria, demonstrates that the tower remains far below its compressive failure limits. The study confirms that the observed inclination—about 56 cm towards the northwest—is not symptomatic of instability but the long-term geotechnical response of the alluvial sediments beneath the cathedral. The research highlights the technical ingenuity of José López in the eighteenth century, who compensated the earlier differential settlement by redistributing loads through asymmetric wall thickening. The tower’s gradual deformation is thus interpreted both as a geophysical record and as a cultural expression of equilibrium between gravity and grace in historic architecture.