ABSTRACT
The construction of Gothic cathedrals is among the great achievements of medieval science as it is defined in terms of theorica and practica. This study introduces the original sources of the Codex of the Cathedral of Tortosa (Catalonia, Spain). A documental survey of masonry books (11.o. ACTo), the Guarc parchment (ca.1345–1380) and the geometric layout of Tortosa Cathedral carried out over the last decade provide some details that afford an understanding of some of the conditions of execution and construction of what has become known as geometria fabrorum. Two main sources allow a bijective assessment of the built masonry: the ACTo chapter archive and the parchment known as la traça de Guarc (ca.1345–1380). These sources show a heptagonal apse with an arithmetical and geometric dimension based on a metrological and tonal musical proportion of 9/8, which is perfectly compatible with the bases of the quadrivium. The lateral and radial chapel, as the basic unit and feature element in 14th-century Gothic cathedral design, can be used as a pattern and its measurement established as the basic unit for the overall proportions of the cathedral.
