GEOMETRIC PROPORTIONING OF THE WIDEST GOTHIC NAVE: BLONDEL'S RULE AND THE BUTTRESS SYSTEM OF GIRONA CATHEDRAL

The Cathedral of Santa Maria of Girona contains the widest uninterrupted Gothic stone-vaulted nave ever constructed, with a clear span of 22.98 m. This exceptional dimension raises a fundamental question regarding the proportional and geometric logic through which medieval builders coordinated vault form and lateral support at an unprecedented scale. This study examines whether the documented transverse geometry of the nave is compatible with the historical buttress-sizing procedure commonly associated with François Blondel, applying his construction directly to the nave intrados and comparing the resulting theoretical buttress depth with the surviving masonry support. The analysis reveals a close geometric correspondence, within the precision of the available graphic sources, between the vertical generated by Blondel's rule and the outer face of the upper buttress body, while the lower masonry projects further outwards, producing an additional basal enlargement beyond the theoretical line. This deviation occurs on the conservative side and indicates proportional compatibility rather than exact geometric coincidence. The result does not demonstrate direct historical transmission of Blondel's formulation, but suggests that Girona's geometry is consistent with a broader tradition of proportional design later codified in architectural treatises. Comparative analysis with selected Gothic cathedrals further shows that Girona's singularity lies not in the use of buttresses alone, but in the exceptional scale at which a continuous wall-and-buttress system was applied to a single uninterrupted nave.