For a century the cathedral had a hole in its roof no one could cover. Here is how a goldsmith raised the largest masonry dome ever built — without scaffolding.
For more than a century, Florence's great cathedral stood with a hole in its roof. The nave was built, the drum was built, and above the crossing gaped an octagonal void nearly 45 metres across that no one knew how to cover. The ancient Romans had raised domes, but their secret — and the timber to centre a dome that size — had been lost. The story of how Filippo Brunelleschi finally closed that gap is one of the great feats of engineering, and you can still climb through the evidence of it today.
When the cathedral's plan was enlarged in the 14th century, it committed Florence to a dome wider than any since antiquity. The catch was structural: a dome that size would normally be built over a vast wooden framework, or "centering", to hold the masonry until it set. No forest could supply timber long or strong enough, and even if it could, the cost was ruinous. So the drum was finished in 1418 and the city held a competition for the one thing still missing.
The goldsmith Filippo Brunelleschi won the commission, reportedly by refusing to reveal his method and instead challenging his rivals to make an egg stand upright on a slab of marble. When none could, he tapped it down to crack its base — anyone can do it once shown, he argued, just as anyone could build his dome once they saw how. He was awarded the work, at first alongside his old rival Lorenzo Ghiberti, though Brunelleschi soon proved indispensable and took sole charge.
Brunelleschi is thought to have studied the ancient Roman ruins — including the Pantheon, whose concrete dome had stood for over a thousand years — before designing his own. But he could not copy it: the Pantheon's dome sits on massive walls, while Florence's had to rise from a high, thin-walled octagon.
Brunelleschi's first great idea was to build not one dome but two, nested one inside the other. The inner shell is thick and structural; the outer shell is lighter and taller, protecting the inner one and giving the profile its soaring outline. The gap between them carries the staircase you climb today — which is why the ascent feels like moving through the dome's structure rather than merely up a tower.
The second idea solved the centering problem. Instead of laying bricks in simple horizontal rings, which would slump inward before the mortar set, Brunelleschi laid them in a self-supporting herringbone pattern. Vertical bricks, set at intervals, locked the horizontal courses in place, so each ring helped hold up the next as it rose. The dome, in effect, supported itself as it was built — and no wooden centering was needed at all.
Raising thousands of tonnes of brick, stone and marble to that height needed machines that did not exist, so Brunelleschi designed them too. His famous ox-hoist used a reversible gear so a single team of oxen could raise or lower loads without being unhitched and turned around — a genuine innovation. He devised load-balancing cranes and platforms that let masons work safely at dizzying heights for the sixteen years the work took.
The dome was closed at its summit in 1436 and the cathedral consecrated that year by Pope Eugenius IV. Brunelleschi went on to design the marble lantern that crowns the whole structure, but died in 1446 before it was finished; it was completed around 1461. He is buried in the crypt directly beneath the dome — and between 1568 and 1579, Vasari and Zuccari covered its interior with the vast Last Judgment you pass on the climb.
Brunelleschi did not have the site to himself. For the early years he was made to share the commission with Lorenzo Ghiberti, the goldsmith who had beaten him decades earlier in the competition for the Baptistery doors. The arrangement galled him, and the old story goes that Brunelleschi feigned illness at a critical moment, leaving Ghiberti unable to direct the work — and exposing how much of the method lived only in Brunelleschi's head. From then on he ran the project alone.
Look up at the very summit and you will see a gilded copper ball and cross above the lantern. It was made in the workshop of Andrea del Verrocchio and hoisted into place in 1471 — and among the young apprentices who helped design the machinery to lift it was Leonardo da Vinci, who sketched Brunelleschi's cranes as a student. The original ball was struck by lightning and fell in 1600; the one up there now is its replacement.
The figures are still staggering. The cupola used something like four million bricks and weighs in the tens of thousands of tonnes, and it remains the largest masonry dome ever built. From the piazza to the top of the cross it rises well over 110 metres, and the inner shell spans roughly 45 metres with nothing holding it up but its own geometry. Nearly six centuries on, it is still the tallest thing in the historic centre.
Perhaps the strangest part is how little Brunelleschi wrote down. Fiercely protective of his methods, he left no complete set of drawings explaining how the dome was raised, and engineers have spent centuries reconstructing his reasoning from the building itself. That secrecy is part of why the climb feels like detective work: the evidence of how it was done is in the brick under your hand, not in a manual.
As you climb, look at the brickwork in the stairwell between the shells: the diagonal herringbone courses are still visible in places. You are, quite literally, walking through the solution to the puzzle that stumped Florence for a hundred years.
Brunelleschi's cupola was not just an engineering fix; it changed what people believed was possible in stone, and it became the emblem of a city remaking itself at the dawn of the Renaissance. Architects came from across Europe to study it, and its silhouette still defines Florence from every hilltop. Michelangelo, tasked centuries later with the dome of St Peter's in Rome, is said to have vowed to make it wider but never more beautiful. When you climb it, you are climbing the building that told the age what human ambition could achieve.
Reading about the dome is one thing; standing inside it is another. The 463-step climb takes you between the two shells, out beneath the frescoes and onto the lantern platform. A guided tour is the best way to make sense of what you are climbing through, and skips the queue — compare the Florence Duomo tours that include the dome, or the dome climb and museum tour, which pairs the ascent with Brunelleschi's original wooden model in the museum.
New to the complex? Start with our guide to the Duomo complex, or decide between the climbs with dome vs bell tower.