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Florence's Cathedral Dome: A Renaissance Success Story

by Charles Freeman

View of the cathedral in Florence. Image: Bruce Stokes, CC BY-SA 2.0

By the early fifteenth century, the cities around Florence were convinced that the Florentines were going to be the laughing stock of Italy. They had started their new cathedral in 1296 and now, many years later, in 1418 there was one last project needed to complete their grand building. The octagonal base of a vast dome was in place but it was far wider than any tree trunk could cover and higher than even the highest roof of a French Gothic cathedral. The Lana, the wool guild, was in charge of the building and they risked looking like fools if they could not fill the enormous space.

Filippo Brunelleschi, master architect of Florence's cathedral dome. Image: Sailko, CC BY 2.5

The Renaissance had seen a renewed fascination with the surviving buildings of ancient Rome. One man, Filippo Brunelleschi, a goldsmith by training, had spent several years in Rome studying the vaults and domes of the city, notably the still intact dome of the first century AD Pantheon. Back in Florence he had already shown himself an innovator when he devised a system for drawing perspectives in art, but when he came forward with a plan to build the dome, the Lana hesitated. While they could understand how he would get started, with vast rings of iron, stone and brick at intervals as the dome rose from its foundations, there would be a moment when the dome would start leaning inwards and might well collapse into the void. ‘No worry’, said Brunelleschi, ‘I will sort that out when we get there.’

The Duomo, as if completed, in a fresco by Andrea di Bonaiuto, painted in the 1360s, before the commencement of the dome

It was a tremendous gamble and no one but an arrogant genius would have had the confidence that he could achieve it. Brunelleschi was given joint control with a former rival, Lorenzo Ghiberti, but Brunelleschi soon pushed him aside. Building began in 1420. First, Brunelleschi had to devise a way of getting his materials up to the starting base. No such lifting device had been constructed since Roman times but Brunelleschi created an oxen-powered cylinder with 600 foot long ropes which could heave up a stone every ten minutes. It became as great an attraction as the dome which the apprehensive citizens could watch steadily rising from across the city. Even when the stones and bricks had been raised high enough they had to be shifted by other devices around the circle of the dome.

Above, left to right: Interior structure of the dome, stairway between the inner and outer domes (Image: Sailko, CC BY 3.0) and plan of the dome, showing the inner and outer domes

Today the stresses would easily be calculated on a computer. If misjudged the building might fall inwards or outwards. Somehow these stresses had to be managed so they tightened the dome rather than caused it to crack and fall. Brunelleschi did it by instinct, thinking of all kinds of imaginative ways of lessening the stresses. He realised that it was best to build an inner dome which did not need to look smart and then build an outer, more elegant, dome outside with space between the two where the workmen could work safely. (Extraordinarily only one workman fell to his death in sixteen years of building.)

The dome as seen from the bell tower. Image: Birasuegi, CC BY-SA 2.0

Recent studies of similar domes that copied Brunelleschi’s methods have discovered how he assessed and lessened the stresses. As the dome rose after the first layers of stone he used bricks. These were lighter than stone and could be moulded to ensure an exact fit wherever they needed to be placed. It is said that Brunelleschi personally examined each one of four million bricks to make sure that each was of the right quality. Ingenious ways of creating herringbone patterns made sure that the stresses flowed sideways and strengthened the stability of the dome. Another problem Brunelleschi solved was how to let the mortar dry without a stone or brick falling off while it did so.

Interior of the dome: Vasari's fresco begun in 1568 and completed by Federico Zuccariin in 1579. Image: Livioandronico2013 CC BY SA-4.0

Finally the dome was almost complete. There had to be a ceremony of inauguration and no less than the pope, Eugenius IV, presided at the mass on the Feast of the Annunciation, March 25th, 1436, sixteen years after Brunelleschi had begun building. There was still the top to be finished off and the Lana decided that it would be a lantern. Ungratefully they arranged a new competition for the design but Brunelleschi won it again. By now the dome dwarfed every other building of the city and Brunelleschi had to construct yet another mechanical device to lift the stone to the top of the dome. This time it had a ratchet so that lifting could be stopped on the way if the weight was too much. Finally, in 1461, the lantern was finished and in 1469 a gold ball was in place at its summit. Brunelleschi had died in 1446 but everyone now acclaimed his genius.

The lantern of the dome. Image: Birasuegi, CC BY-SA 2.0

I have climbed the dome a number of times in my life. In fact, I clamber up within the two domes most times I am in Florence (not least to show that I can still do it fifty-four years after my first visit!). There is a wonderful view over the city from the balcony and any painting of Florence since the fifteenth century shows the dome dominating the city landscape.

In my new book The Awakening, A History of the Western Mind, AD 500-1700, I highlight it as a one of the great successes of the Renaissance. It is not only an extraordinary construction by one individual genius, the first architectural project of this size for over a thousand years, but an act of supreme confidence by the arrogant Florentines. Now they could rightly flaunt their achievement over their rivals.


About the Author

Charles Freemanis a specialist on the ancient world and its legacy. He has worked on archaeological digs on the continents surrounding the Mediterranean and develops study tou r programs in Italy, Greece, and Turkey. Freeman is Historical Consultant to the Blue Guides series and the author of numerous books, including the bestseller The Closing of the Western Mind and, most recently, Holy Bones, Holy Dust. He lives in the UK. His latest book, The Awakening, A History of the Western Mind, AD 500-1700 is published by Head of Zeus on 6th August 2020.


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