The Great Dome of Florence

The city of Florence came late to the business of building cathedrals. Neighboring cities like Siena, Pisa, and Lucca already had great cathedral churches by the time the Florentines decided to build themselves a new one in the 1290s. For most of its life before the 13th century, Florence was a small backwater on the Arno river barely worth mentioning next to a major port city and sea power like Pisa. At the beginning of the 13th century, it was a small town built on the remains of a Roman military settlement in the mosquito infested Arno river valley. By the end of the 13th century, Florence was one of the major cities of Europe, rivaling Paris and London in size and importance. What accounted for the city's sudden greatness? Business; Florence was history's first great boom town, built on industry and commerce, the textile industry and banking, instead of the usual trade and conquest. And with it came all the familiar stresses of sudden wealth and expansion, including one of history's first major labor uprisings, the Ciompi rebellion. The workers in the city's booming and vital textile industry rose up and briefly seized power in the city in the late 13th century.

Florence Baptistery.

For almost 3 centuries, Florence's revered 11th century Baptistery served as the city's cathedral church. A lot of local lore surrounds the church. Tradition says that Charlemagne built the church on his return from his coronation in Rome (not true, Charlemagne was dead 2 centuries before this was built). Another tradition says that the Baptistery stands on the site of a temple to Mars built by Julius Caesar (there may be some truth to this; recent excavations in the floor revealed what may be the remains of a Roman temple). A number of local saints are associated with the building.  St. Zenobius worked miracles here, and local martyr St. Reparata was buried near here.

Dome of the Florence Baptistery.

Inside the Baptistery is a great octagonal dome with a major masterwork of Italo-Byzantine art, the dome mosaic of the Last Judgment, with scenes from Genesis, the story of Joseph, and the life of John the Baptist, the city's patron saint. Italy was under Byzantine rule only briefly, but the Byzantine style, the Maniera Greca, in art remained dominant in Italy for centuries.

By the end of the 13th century, the Baptistery became too small to serve as the cathedral of a major city. The city decided to build a new one just east of the Baptistery where the church of Santa Reparata stood. That church was torn down and a large tract of land was cleared to the east to make room for a huge new cathedral.

The Florentines decided to make a big cathedral, the biggest in Europe. What is more, they wanted the dominant feature of the new cathedral to be something very distinct, announcing the Roman origins of their city. Instead of a great tower or spire, the Florentines decided to top their cathedral with a dome, the largest dome built since the completion of the Pantheon in Rome, and preferrably bigger.

The proposed Cathedral of Florence, detail from the 14th century fresco "The Church Militant and Triumphant" by Andrea di Firenze.

Construction proceeded very quickly and successfully on the cathedral. Its size began to stir feelings of envy and rivalry among some of the older surrounding cities. Siena decided to more than double the size of its cathedral transforming the present cathedral into transepts for a huge new church.

Interior of the nave of Florence Cathedral.

The sculptor Arnolfo di Cambio was probably responsible for the design of the nave of the new cathedral with its long ribbed vaults, the longest in Europe. The painter Giotto designed the new campanile or bell tower.
The catastrophe of the Black Death did nothing to stop or even slow down the construction of the cathedral. Florence lost half its population in the summer of 1348, and yet the pace of construction only accelerated. The plan was altered to make the proposed dome even bigger. Florence survived and recovered from the Black Death. Siena did not. Work stopped on its cathedral expansion, and the unfinished remains of the nave of the proposed cathedral stand next to the present Cathedral of Siena.
Work continued on the cathedral even through 2 potentially lethal wars with the Duke of Milan. During the second, the Duke laid siege to the city and all seemed lost. Then plague broke out in the Milanese encampment killing off much of the Milanese army and the Duke himself. The Florentines considered this a sign from God that He favored their city and its stubborn opposition to efforts to unify Italy under a single ruler. By the beginning of the 15th century, there was a kind of Florentine patriotism and ideology. Florence saw itself as a divinely favored champion of republican liberty against the monarchs of Europe; David standing against Goliath.

Apse and dome of the Cathedral of Florence from the nave.

Toward the end of the 14th century, construction on the cathedral stopped. It stopped not because of any catastrophe, or any shortage of money or will, but because no one knew how to build the dome. No one could figure out a safe and economically viable way to build the dome. And so for decades, the great yawning space over the high altar remained open to the wind and rain until someone could figure out how to build it.

Centering used to build the arch of a stone bridge in the 19th century.

Since Roman times, centering -- a wooden framework -- was used to build arches, vaults, and domes. The Romans invented structural concrete, which could be poured into molds and dry hard and strong, to span vast interior spaces with vaults. Concrete was very strong and relatively lightweight. Builders forgot the process for making concrete in the Dark Ages. It would not be reinvented until the 16th century for the construction of St. Peter's in Rome. The dome of the Cathedral of Florence would be built of much heavier brick and stone. Adding to the difficulty, the proposed dome vault was not spherical, but octagonal like the dome of the Baptistery. To build the dome using conventional centering would require the deforestation of central Italy. In addition, there were no trees in Italy, or in much of the rest of Europe, tall enough to reach up to the 200 foot height where the dome would begin, or to reach across its vast span.

Filippo Brunelleschi

In about 1410, the Opera del Duomo (the Works of the Cathedral) held a competition to see who could come up with a viable plan for finishing the dome of the cathedral. Among the entrants was a very unlikely candidate, a middle-aged, short, balding, bad tempered, man with a very weak resume. Filippo Brunelleschi was a silver-smith, sculptor, clock-maker, and surveyor with expertise in mathematics and optics. He had no building experience. He was humiliated 10 years earlier in the competition to see who would make bronze doors for the Baptistery. He barely lost out to Lorenzo Ghiberti. After losing the competition, he left Florence for self-imposed exile in Rome vowing never to return.
And now this difficult tempermental man was back with his proposal to finish the dome. He said that he could build the dome with a minimal amount of scaffolding and without the use of traditional centering. The Opera was very impressed with his plans and models, with the whole proposal. It was daring, but much more credible than any of the other proposals they had. They gave Brunelleschi the job, but because of his weak curriculum vitae, they made his old arch-enemy Lorenzo Ghiberti (now the most successful sculptor in Italy) a partner in the whole enterprise.

Section plan of the Cathedral of Florence, 17th century engraving.

Brunelleschi proposed that the dome be self-supporting as it rose on its 14th century base. Scaffolding would rise as the dome rose. To move large amounts of stone and brick up to the 200 foot height to build the dome, Brunelleschi built an enormous wooden construction boom -- the first of its kind and the direct ancestor of the modern construction boom -- in the center of the cathedral's dome space.
In terms of both engineering and design, the dome Brunelleschi built is a hybrid. It is a classical Roman form built with medieval methods and modified by medieval design and usage. He designed a double-shell dome of brick with a large space between the two shells. This lightened the load on the rest of the cathedral, and made the structure flexible as the building settled. Between those shells is a system of brick ribs and struts that carry most of the building's structural stresses, very much like the ribs and buttresses of a Gothic cathedral, or even like the struts and ribs in the wing of an old biplane.

Passage between the 2 shells of the dome of the Florence Cathedral.


Part of the complex brick pattern designed by Brunelleschi. The bricks are laid in a complex spiraling herring bone pattern so that they support each other by their own weight.

Florence Cathedral dome from the east.

The design as well as the structure of the dome is a hybrid of Gothic on a Roman building form. Instead of the Roman hemispherical shell, the dome of the cathedral is a pointed ribbed octagon. Its steep profile against the sky inspired many centuries' worth of imitations and adaptations, most famously Michelangelo's design for the dome of St. Peter's in Rome.
The tiny structure at the top is called a lantern. So far as I know, this is the first one on any dome.

Interior of the dome with paintings added over a century after completion.

Oculus of the dome. Brunelleschi spent his ten years in exile studying Roman construction techniques and Roman monuments, especially the Pantheon. Like that building, Brunelleschi's dome culminates in an opening to the sky. Unlike its Roman prototype, Brunelleschi built a structure above the oculus to let in the sunlight and keep out the rain and pigeons, the lantern.

This is a structure that magnificently and concisely summarizes the whole history of the city of Florence: its Roman foundations, its religious heritage embodied in the revered Baptistery, and its late medieval greatness. It proclaims the religious and political ideology of the Florentine Republic to the world and to history.

The dome was completed in 1436. All the great and mighty of Italy, including Pope Eugene IV, arrived for a magnificent consecration ceremony. In the midst of that gathering of the powerful, Brunellechi met and made close friendship with one minor secretary in the large retinue of an attending cardinal, a low level clerk named Leon Battista Alberti.
Alberti dedicated his book On Painting to Brunelleschi and included this tribute in the introduction:

Who is so stubborn or so envious that he would not praise Pippo [Filippo] the architect, when he sees such a big building here, set aloft above the heavens, ample to cover all the peoples of Tuscany with its shade, made without any aid from scaffolding or quantity of timber? -- a skillful construction which, if my opinion is right, as in our times it was unbelievable that it could be done, so among the ancients it was perhaps not known or known about.

The Bells of Florence Cathedral.

Twenty years ago, I left a rose at Brunelleschi's tomb in the Cathedral of Florence. I plan to leave another one with him next week when I visit Barbara Crafton in Florence and see the old town for the first time in 20 years.
When I return, I will begin a semester as a new full time art and art history teacher at Bronx Community College.