Once erection of the walls was completed, assembly of the roof could commence. The flat or gabled roofs were held up by square, evenly-spaced wood beams, which carried the weight of the roof and ceiling (if one was present). In the sanctuaries it was common for beams to be decorated with painted designs. Vigas rested on wood corbels, which were built into the walls and often projected on the outside of the building. When the rafters were in place a thatch of "tules" (brush) was woven over them for insulation, and were in turn covered with clay tiles. The tiles were cemented to the roof with mortar, clay, or "brea" (tar or bitumen). At some of the missions the padres were able to hire professional stonemasons to assist them in their endeavors; in 1797, for example, master mason Isidoro Aguílar was brought in from Culiacán, Mexico to supervise the building of a stone church at San Juan Capistrano. The church, constructed mostly of sandstone, featured a vaulted ceiling and seven domes. Indians had to gather thousands of stones from miles around for this venture, transporting them in carrettas or carrying them by hand. This structure, nicknamed "Serra's Church" once had a l20-foot-tall bell tower that was almost totally destroyed by in 1812.