Wooden scale model 1:25 by Franco Gizdulich  (2015) illustrating the structure of Brunelleschi’s dome. The model helps to understand the various techniques Filippo Brunelleschi used to build the dome of the Cathedral. Here we can see how it actually consists of two shells or layers, an internal one of even thickness, and another outer shell tapering progressively upwards. Each sail of the dome is delineated by ribs, but is also strengthened by two intermediate ribs, as well as horizontal chains lashing the ribs together.