the Duomo

the Duomo, Roman Catholic church in Florence, Italy. When it was consecrated in 1436, it was the world’s largest church, able to accommodate 30,000 worshippers. Among the building’s significant features are its stained-glass windows; its ornate green, red, and white marble facade; its collection of paintings and statuary by Renaissance masters; and especially its dome, designed by Filippo Brunelleschi (1420–36).

The construction of the building—built on the site of the old cathedral of Santa Reparata—was overseen by several architects, beginning with Arnolfo di Cambio in 1296. After his death the following decade, construction slowed until 1331, when the Arte della Lana (guild of wool manufacturers and merchants) assumed responsibility for the building. In 1334 the guild appointed painter and architect Giotto as master builder, assisted by architect Andrea Pisano. Following Giotto’s death in 1337, a number of architects took the lead, and plans were made to enlarge the original project and build a dome. By 1418 construction had reached the stage at which the technical problems of building a vault above the enormous dimensions of the dome had to be solved. A competition was subsequently held to find a design, and the winner was Brunelleschi, a sculptor and architect whose innovative plan was self-supporting, requiring no scaffolding. He was named chief architect (capomaestro) of the dome project in 1420 and remained in that office until his death in 1446.

Brunelleschi’s dome consists of two layers: an inner shell spanning the diameter and a parallel outer shell to protect it from the weather and give it a more pleasing external form. Both shells are supported by 24 stone half arches, or ribs, which taper and meet at an open stone compression ring at the top. Only eight of the ribs are visible on the exterior, giving the dome an octagonal shape recalling the nearby 11th-century Baptistery of San Giovanni. To resist outward thrust, tie rings of stone held together with metal cramps run horizontally between the ribs. There are also tie rings of oak timbers joined by metal connectors. The spaces between the ribs and tie rings are spanned by the inner and outer shells, which are stone for the first 7.1 metres (23 feet) and brick above. The entire structure was built without formwork, the circular profiles of the ribs and rings being maintained by a system of measuring wires fixed at the centres of curvature. Brunelleschi obviously understood enough about the structural behaviour of the dome to know that if it were built in horizontal layers, it would always be stable and not require timber centring. He also designed elaborate wooden machines to move the needed building materials both vertically and horizontally.

By 1436 the structure was mostly realized, though Brunelleschi’s lantern, the small cupola-like structure mounted on top of the dome to admit light, was not completed until after his death. The building’s dome belongs within the Gothic tradition, as it was built with rib construction and a pointed arch form, but the introduction of a drum, which made the dome more prominent, became characteristic of the Renaissance dome. Having all but equaled the span of the Pantheon in Rome in stone, Brunelleschi was hailed as the man who “renewed Roman masonry work.” The massive octagonal dome continued to dominate both the church and the city in the 21st century.