The Problem of Erecting the Main Dome and Roof Vaults of the Church of San Xavier Del Bac

Little evidence has been uncovered regarding the facts of construction of the church of San Xavier del Bac, aside from the letters of Father Francisco Inturralde which reported in 1797 that construction and decoration were complete (Fontana 1963). Judgments concerning the methods of the church builders and artisans must be based on our knowledge of the technology used in New Spain and by the medieval cathedral builders of Europe. Occasionally the church itself yields visual clues to methods of its construction. Such was the case with respect to several holes found in the walls of the nave and main dome, shedding light on the problem of determining how domes over the crossing and sacristy and the low roof vaults were erected. This paper considers several visual clues in the church structure pointing to alternative methods of dome and vault construction and explaining the builders' solution to the problem of constructing a round dome over San Xavier's square transept crossing.