Construction Begins on Brunelleschi's Dome
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 brilliant masonry techniques were Brunelleschi's spectacular contribution to architecture. The ability to transcribe a circle on a cone face within the innermost double-shelled wall makes the self-sustaining "horizontal" arch construction possible, since geometrically, a circular plan is needed for such an erection.
Ghiberti, appointed coadjutator, mocked these plans and called them unfeasible. Brunelleschi, deeply offended, then pretended a sickness and left for Rome, leaving the project in the hands of Ghiberti. But Ghiberti soon had to admit that the whole project was beyond him. In 1423 Brunelleschi was back in charge and took over sole responsibility.
Work started on the dome in 1420 and was completed in 1436. The cathedral was consecrated by Pope Eugene IV on March 25, 1436 (the first day of the year according to the Florentine calendar). It was the first 'octagonal' dome in history (The Roman Pantheon, a circular dome, was built in 117–128 C.E. with support structures) to be built without a wooden supporting frame and was the largest dome built at the time (it is still the largest masonry dome in the world). It had been one of the most impressive projects of the Renaissance. During the consecration service in 1436, Guillaume Dufay's similarly unique motet Nuper rosarum flores was performed. The structure of this motet was strongly influenced by the structure of the dome.
Brunelleschi's ability to crown the dome with a lantern was questioned and he had to undergo another competition. He was declared the winner over his competitors Lorenzo Ghiberti and Antonio Ciaccheri. His design was for an octagonal lantern with eight radiating buttresses and eight high arched windows (now on display in the Museum Opera del Duomo). Construction of the lantern was begun a few months before his death in 1446. Then, for 15 years, little progress was possible, due to alterations by several architects. The lantern was finally completed by Brunelleschi's friend Michelozzo in 1461. The conical roof was crowned with a gilt copper ball and cross, containing holy relics, by Verrocchio in 1469. This brings the total height of the dome and lantern to 114.5 metres (375 ft). This copper ball was struck by lightning on 17 July 1600 and fell down. It was replaced by an even larger one two years later.
Brunelleschi knew that there was not enough timber in Tuscany to build a scaffold inside the Cathedral, and the recipe for concrete had been lost since the fall of Rome. Brunelleschi instead came up with an ingenious and completely original theory. His plans showed an inner hemispherical dome within Florence cathedral's octagonal drum. A second, ovoid brick dome was to be placed on top, and nine sandstone rings would then hold the structure together, like a barrel. To raise the bricks and sandstone beams several hundred feet in the air, Brunelleschi invented a fast and efficient hoist with the world's first reverse gear, allowing an ox to raise or lower a load at the flick of a switch.