Brunelleschi’s dome is the roof of the cruise of the Florence Cathedral; at the time of construction it was the largest dome in the world and still remains the largest masonry dome ever built (the maximum diameter of the internal dome is 45.5 meters, while that of the outside is 54.8). Thanks to the fundamental importance it had for the subsequent development of architecture and the modern conception of building, it is still considered by some to be the most important architectural work ever built in Europe since Roman times.
Its size prevented the traditional construction method with the aid of ribs, causing many hypotheses to be formulated on the construction technique used.
The drum, of imperfect octagonal shape, on which the dome was supposed to rest, measured about 45 meters wide on the largest diagonal and was 54 meters high. These dimensions were considerably larger than originally predicted. The reasons for this increase, which led the size of the building to exceed those of the dome of the Pantheon, until then the largest dome in the world, so much so that legend considered it the work of the devil, are to be found not so much in the desire for primacy, but in the need to reinforce the dome drum as much as possible. The drum had in fact been raised with respect to the original model by means of a plane in which eight large eyes open, which favored the illumination of the cathedral’s apse triconco. With this expedient the dome’s tax plane was also raised above all the vaults built up until then. The very high vaults of the cathedral of Beauvais in France, which for their boldness collapsed shortly after their construction, reached “only” 48 meters in height. But the irregular octagonal shaped drum also created the main obstacle to the erection of the dome. Brunelleschi calculated every detail with precision, from the inclination of the walls to the arrangement of the herringbone bricks. In this way the dome was able to support itself, without resting on the traditional sulphurous wooden scaffolding.