How was Brunelleschi's dome built?

The full story is juicier. Florence had a huge cathedral, an eight-sided gap nobody knew how to roof, and one man who proposed doing it without a frame. They took him for a madman.

Why was it so difficult?

Florence's new cathedral, Santa Maria del Fiore, was founded in 1296. How to cover that gap had caused bitter arguments among several generations of architects, and the usual method, centring, the wooden framework that holds a vault up until it's closed, simply wouldn't work for a span and a weight like that.

The answer came from someone who had once lost a competition.

Who was Brunelleschi? The loser of 1401

In 1401 a competition was held for a set of bronze doors for the Baptistery of San Giovanni, opposite the cathedral. Each entrant had to submit a relief on the same subject: the sacrifice of Isaac. Two young men were among the candidates: Lorenzo Ghiberti and Filippo Brunelleschi.

Ghiberti got the commission. In his memoirs he boasts that every expert and every rival gave him the victory. The other versions don't agree. Giorgio Vasari, the great biographer of Renaissance artists, says Brunelleschi and Donatello persuaded the judges that Ghiberti's was the best, and that Filippo refused to share the work; the life of Brunelleschi attributed to Antonio Manetti talks of a shared victory. Everyone told the version that suited them.

Remember those two names. Seventeen years later their paths would cross again, this time a good deal higher up.

How did he win the job? A model with no frame

On 19 August 1418 a competition was announced for models of the dome. Ghiberti and Brunelleschi both entered. Ghiberti's model relied on the good old wooden centring. Brunelleschi's, worked out with Donatello and Nanni di Banco and built in masonry next to the bell tower at the end of that year, had the big new idea: it needed no frame at all.

Vasari, whose Lives came out more than a century later (we're following the 1568 edition), turns this into comedy. According to him, when Filippo explained that he'd build the dome double-shelled and without a frame, the men in charge thought he'd lost his mind. He insisted so hard that the ushers ended up carrying him bodily out of the room. For a while, Vasari says, Filippo didn't dare show his face in the street, dreading people saying behind him, "there goes the madman".

Is the story of Brunelleschi's egg true?

Then comes the scene everyone knows. Vasari tells us the assembled masters wanted to see Filippo's model and he refused to show it. Instead, he set them a challenge: the dome should go to whoever could make an egg stand upright on a slab of marble. They all tried, and all failed. Then he tapped the bottom of the egg against the marble and stood it up. The others protested that they could have done that. And Filippo, laughing, told them that if he showed them his model, building the dome would look just as easy.

But note: Vasari himself introduces the anecdote with "it's said". Not even he vouched for it. The egg is a legend, and a very good one, but it isn't what won Brunelleschi the dome.

Who won, Brunelleschi or Ghiberti?

What actually happened was messier. The result was declared a tie and the two rivals were told to work together. From 1420, Brunelleschi and Ghiberti jointly supervised the building of the dome.

Vasari claims Filippo came close to leaving Florence, and that it took two friends, Donatello and Luca della Robbia, to talk him round. Then, still according to Vasari, came the revenge. One day Filippo didn't turn up for work. He took to his bed, bandaged his head and said he had a pain in his side. The masters went to ask Ghiberti what to do, he wouldn't decide anything without Filippo, and the work ground to a halt. When they came to fetch him, Filippo answered from his bed: "Voi avete Lorenzo, faccia un poco egli". In other words: you've got Lorenzo, let him get on with it. Then he proposed splitting the work, the scaffolding for himself and the reinforcing chain for Ghiberti, and Ghiberti's part was judged inadequate.

Did it happen like that? The records say nothing about the fake illness, and Vasari gets his dates in a muddle telling it. But they do confirm how it ended. In a document of 1423, Brunelleschi alone is named inventor et ghubernator maior of the dome: its inventor and chief director. And from 1426, Ghiberti's work on the building was cut to one hour a day, while Brunelleschi worked full time on a handsome salary. The comedy is Vasari's; the victory is in the paperwork.

How does it stand up without a frame?

The key was giving up the centring, which was exactly what was new about his 1418 model. The dome went up senza armadura, without that frame, course by course: the bricks were laid in herringbone and each section held itself up as the work rose. Vasari adds that Filippo designed it as a double dome, another idea that sounded absurd at the time. It was completed in the 1430s and consecrated in 1436, and Brunelleschi stayed in charge as master builder until his death.

What about the lantern and the ball on top?

It still needed crowning with the lantern, the small marble tower at the very top. Vasari says many experts believed the dome couldn't bear such a load, and that piling that much weight on it was tempting God. Filippo just laughed. He never saw it finished: the lantern was built by Michelozzo after 1446, once Brunelleschi had died.

Vasari also wrote that it seemed as if heaven envied the dome, because lightning struck it again and again. In May 1471 a gilded copper ball made by Andrea del Verrocchio, more than two metres across, was hoisted onto the lantern. One winter's night in 1601, lightning brought it down into the square. A marble disc in the paving marks, so they say, the spot where it landed.

Fact or legend.

• On record: the 1418 competition, the tie and the shared post; Ghiberti cut to an hour a day from 1426; Brunelleschi named "inventor and chief director" in 1423; the dome built without centring, in herringbone brickwork, completed in the 1430s and consecrated in 1436; the lantern completed after his death.
• Vasari's account (in the 1568 edition of his Lives; not backed up by the records): the "madman" carried out of the room, the flight prevented by Donatello and Luca della Robbia, and the fake illness.
• Legend: the egg. Vasari himself tells it with an "it's said".
• Conflicting versions: who really won the 1401 competition for the doors.

Where to hear it

The story of the dome is told on Podtour's free route in Florence, "The Duomo and the Baptistery", at the stop "Brunelleschi and the egg". The rivalry begins earlier, in front of the Baptistery doors, at "A competition with a trick", and the golden ball brought down by lightning has a stop of its own, "The ball that fell from the dome". Every stop is heard from the square.

If you're planning your trip, our Florence guide has the practical side covered.

Further reading

• Giorgio Vasari, Le vite de' più eccellenti pittori, scultori e architettori, "Filippo Brunelleschi", Giunti, 1568; transcription on Wikisource (in Italian). https://it.wikisource.org/wiki/Le_vite_de'_pi%C3%B9_eccellenti_pittori,_scultori_e_architettori_(1568)/Filippo_Brunelleschi
• "BRUNELLESCHI, Filippo", Dizionario Biografico degli Italiani, vol. 14, Istituto della Enciclopedia Italiana (Treccani), 1972 (in Italian). https://www.treccani.it/enciclopedia/filippo-brunelleschi_(Dizionario-Biografico)/
• Carlo La Bella, "GHIBERTI, Lorenzo", Dizionario Biografico degli Italiani, vol. 53, Istituto della Enciclopedia Italiana (Treccani), 2000 (in Italian). https://www.treccani.it/enciclopedia/lorenzo-ghiberti_(Dizionario-Biografico)/
• Lorenzo Ghiberti, I commentari, second book (c. 1447–1455), on Wikisource (in Italian). https://it.wikisource.org/wiki/I_commentari,_secondo_libro
• Maurizio Costanzo, "Firenze, quando la Palla d'oro del Duomo cadde dalla cupola", La Nazione, 18 January 2025 (in Italian). https://www.lanazione.it/firenze/cupola-duomo-firenze-e31bad31