Brunelleschi completes the dome

The story

A church without a dome

In 1296 the Florentines decided to build the biggest and most beautiful church in the city, the cathedral of Santa Maria del Fiore, to show the world the wealth and pride of Florence. The architect was Arnolfo di Cambio. Work went on for more than a century: the façade, the aisles and the bell tower designed by Giotto were built. At the centre there was meant to be an enormous dome, but nobody knew how to build it.

By the start of the 15th century the great eight-sided drum on which it was to rest had already been built: an opening about forty-five metres wide, almost the size of a town square, more than fifty metres up in the air. Nobody since the Romans had covered such a large space. Centrings, the wooden scaffolds that normally hold up a dome while it is being built, were not possible: there were not enough big trees, and the cost would have been huge. For years the great church stayed open to the sky, and the Florentines wondered whether the dome would ever be finished.

The competition of 1418

In 1418 the Opera del Duomo, the body in charge of the work, announced a competition open to everyone: whoever found a way to build the dome would win a prize and the job. Architects and engineers came from all over Italy and from other countries too, with ideas that were sometimes bizarre. One suggested filling the church with earth mixed with coins, so that people, to get the money, would carry the earth away.

Among the competitors was Filippo Brunelleschi, a goldsmith and former clockmaker, who had been to Rome to study ancient monuments such as the Pantheon and who knew geometry. The story goes, in Vasari's biographies, that when he refused to show his plan, for fear that it would be copied, the judges threw him out. Then, according to the anecdote, to explain himself, he challenged the other architects to make an egg stand upright on a slab of marble: nobody managed it; he tapped the egg on the marble, crushing its base, and left it standing. “But anyone can do it like that!” they said. “You could also have built the dome, if you had seen my model,” he replied.

A double dome with no scaffolding

Brunelleschi's idea was brilliant: to build the dome without big centrings, making sure that each ring of bricks supported itself as it rose. To do this he designed a dome with a “double shell”: a thicker inner shell and a lighter outer shell, with an empty space in between, where you can walk on stairs and corridors. The shape was a pointed arch, more upright than a half-circle, because it pushes less outwards.

The bricks were laid in a “herringbone” pattern, that is, with a series of bricks set on edge between the horizontal courses, so as to lock the courses together and stop them slipping: this made it possible to build even without supports. Chains of stone and wood were placed around the dome to hold it together, like the hoops of a barrel. About four million bricks were used.

Machines and building site

Brunelleschi also invented machines for lifting materials: a great crane driven by oxen, with a clever system of gears to change direction, which made it possible to lift marble blocks and wooden beams high up, even a hundred metres, without having to turn the oxen round. For the bricklayers, who worked dozens of metres above the ground, fixed scaffolds were built and, so that no time was lost coming down to eat, small taverns were opened up high: the workers drank a little wine and went back to work.

The work began in 1420 and went on amid obstacles and jealousy. Ghiberti, the rival sculptor, was named co-director, even though he actually had little experience. Brunelleschi managed to get himself recognised as the only head. In 1436, on 25 March, the day the Florentine year began, the dome was finished, and Pope Eugene IV consecrated the cathedral with a solemn ceremony. The lantern, the structure at the top, was built afterwards and completed in 1461.