By the beginning of the fifteenth century, the drum of the church was built. However, the 42 meter wide space above the church's chancel still did not have the planned octagonal cupola, even though a brick model from 1367 already existed (as related in the "Life of Brunelleschi" by Antonio Manetti, ca. 1480).
In 1419, the Arte della Lana held a competition to design a dome and cupola for the cathedral. The two main competitors were Lorenzo Ghiberti (famous for his work on the "Gates of Paradise" doors at the Baptistery) and Filippo Brunelleschi who was supported by Cosimo de Medici, with Brunelleschi winning and receiving the commission.
The building of a stone dome posed many technical problems. Though Brunelleschi drew his inspiration from the great dome of the Pantheon in Rome, the formula for concrete had long since been forgotten. He would have to build the dome out of bricks. To show what his dome was to look like, he constructed a wooden and brick model with the help of Donatello and Nanni di Banco (on display in the Museum Opera del Duomo). Brunelleschi won by a nose. His model served as a guide for the craftsmen, but was intentionally incomplete, as to ensure his control over the construction.
Brunelleschi's solutions were ingenious and unprecedented: the distinctive octagonal design of the double-walled dome, resting on a drum and not on the roof itself, allowed for the entire dome to be built without the need for scaffolding from the ground, the first large dome ever to be built without centering But, because the dome rested on a drum with no external butresses supporting it, there could be no lateral thrusts at the base of the dome.
This enormous construction weighs 37,000 tons and contains over 4 million bricks. He made several models and drawings of details during the construction. Brunelleschi had to invent special hoisting machines and lewissons for hoisting large stones. These specially designed machines and brilli...