Geometry and Construction of Ribbed Vaults: Choir of the Braga Cathedral

Abstract

The study takes into account the choir vault of the Braga Cathedral as a paradigmatic example of the evolution process of Portuguese multi-ribbed vaults. In fact, it can be considered the first step of the features transmigration occurred throughout the Iberian Peninsula and evolved in a continuous transformation from building to building. The stylistic/typological interpretation, as it is often conducted, is not exhaustive for what concerns stone vaults: conception and meaning of subtended space, construction processes and methods of form definition are essential to read the structure. The study of late Gothic ribbed vaults fits into the research field of structural interpretation from the perspective of “form generators”: this type of construction realizes a strict correspondence between the two aspects, materializing system stress lines through the rib. We analyze one of the first work attributed to Joao de Castilho. The cabeceira of the Braga Cathedral clearly shows traits inherited from ribbed vaults with petal flowers design, typical of Seville and Burgos areas. The various aspects that define the shape are mutually interpenetrating and inseparable: geometric definition, surfaces analysis, underlying spatiality and, finally, the way in which these three are connected to the constructive process. The possibilities of the ribbed lattices are achieved here by a sort of "sphericity research", as if to mediate Gothic reminiscences with the desire to absorb new Renaissance influences. The spatiality research is not an end in itself but can be considered, at the same time, result and assumption of precise constructive methods, giving rise to a logical sequence of steps connected to the building site economy.