Florence Cathedral Dome

The dome of Florence Cathedral (Santa Maria del Fiore) is one of the great engineering achievements of the Renaissance. Designed by Filippo Brunelleschi and built between 1420 and 1436, it covers the octagonal crossing of the cathedral and dominates the city's skyline.

The problem

The cathedral's octagonal crossing was very wide, and the dome followed a design drafted by Neri di Fioravanti some fifty years earlier, but no one knew how to build it. Conventional practice would have needed a huge timber framework (centring) to support the masonry until it was complete.

The competition

On 19 August 1418 the wool merchants' guild (Arte della Lana) announced a design competition. Brunelleschi won over his rival Lorenzo Ghiberti and received the commission.

Construction

• Work began in 1420 and the dome was finished in 1436. Pope Eugene IV consecrated the cathedral on 25 March 1436.
• The dome was the first octagonal dome built without temporary wooden supporting centring.
• It has an inner shell and a thinner outer shell, both of brick, linked by ribs. Brick was chosen because it is lighter than stone.
• Brunelleschi laid bricks in a herringbone pattern so that freshly laid courses transferred their weight to the nearest ribs and did not slide inwards.
• More than 4 million bricks were used, and about 37,000 tons of material were lifted. A 1983 analysis estimated the dome's weight at about 25,000 tons.
• Brunelleschi designed new hoisting machines to raise the materials.

Size

Sources give the internal span as about 42-44 m (138-144 ft), comparable to the Pantheon. With its lantern, the dome stands about 114.5 m (376 ft) high.

The lantern

Brunelleschi designed the lantern on top, and construction began a few months before his death in 1446. Michelozzo completed it in 1461, and Andrea del Verrocchio added the gilt copper ball in 1469.

Legacy

The dome remains the defining landmark of Florence and a standard case study in the history of structural engineering, showing how a very large masonry vault could be raised without full-height timber support.