Monday, August 4, 2008

Florence Cathedral dome

The dome of the cathedral church of Santa Maria del Fiore (St. Mary of the Flowers) in Florence, Italy, was designed and built by Filippo Brunelleschi (1377–1446) in the beginning of the fifteenth century. Towering over the immediately surrounding buildings and still visible, almost 600 years later, from any part of the city, it is one of Europe’s greatest architectural and engineering achievements—a masterpiece of structural ingenuity.
Brunelleschi’s dome completed the building, which had been started in September 1296 by the architect Arnolfo di Cambio. Arnolfo’s original design, which included a much lower cupola, went through many changes, although it is probable that his general plan was retained. Work ceased when he died in 1310, and did not resume until 1331, when the powerful Wool Merchants Guild assumed responsibility for construction. In 1334, simply because he was “a very great man,” the painter Giotto di Bondone was appointed capomaestro to Florence Cathedral, and he designed the freestanding 278-foot (85-meter) bell tower near the southwestern corner of the church. Not finished until two years after his death in 1337, the characteristically Florentine building is faced—as is the church itself—with geometric patterns of red Siena, green Prato, and white Carrara marbles. It was later enriched with relief panels by Luca della Robbia and Andrea Pisano.

The cathedral was beleaguered by further delays caused by political intrigue, a capricious economy, and not least, in 1348, an outbreak of plague that halved the city’s population. The following year Francesco Talenti was appointed to oversee the work. Apart from completing the bell tower, he continually revised the design, working in conjunction with Giovanni di Lapo. Talenti’s “final” scheme evolved by 1366–1367: the nave, flanked by single aisles, was articulated in four square bays leading to an octagonal sanctuary, from which four chapels radiated. Construction work was well in hand by 1370; the nave vaults were finished in 1378 and the aisles a year later. Important in Talenti’s design was a huge octagonal dome over the sanctuary, and construction of its drum had been commenced.

In 1417 a committee, the Opera del Duomo, was charged with the monumental task of building the dome. In 1418 Brunelleschi, who had been recently engaged in bridge building in Pisa, was commissioned to act as adviser. But soon after that the project again lapsed. The dome presented a seemingly impossible problem for the builders because not only did it have to span 135 feet (41.5 meters), but it also had to begin nearly 180 feet (55 meters) above the floor. Nothing of the kind or size had been built since the Roman Pantheon about 1,300 years earlier. A competition was announced, and at a March 1419 meeting, solutions were offered by invited master masons from Italy, France, Germany, and England. None was satisfactory. It was impossible to construct scaffolding to support traditional centering at such a height. Supporting permanent masonry piers were out of the question because they would clutter the sanctuary, blocking the view to the high altar and defeating the purpose of the cathedral. Someone even suggested that the sanctuary should be filled with a mixture of earth and coins to enable the erection of scaffolding; then, when the dome was complete, the citizens of Florence could remove the soil as they dug for the buried treasure. Brunelleschi asserted that he could build the dome without confronting any of these problems.

At first, the committee was skeptical, and when he excitedly defended his position, he was forcibly removed from their meeting. Given another chance to present his proposal, he was reluctant to reveal details. His biographer Giorgio Vasari recounts a delightful anecdote: producing an egg and a thin marble slab, Brunelleschi challenged anyone there to balance the egg on the slab. No one could, and the items were returned to Filippo. He cracked the egg, and stood it upright. To the protest “We could have done that!” he replied, “That’s what you will say if I tell you how I will build the dome!” He was given the commission.

What qualified this sculptor, who trained as a goldsmith, studied science and mathematics, and dabbled in clock making, engineering, and architecture, to confidently undertake such a daunting project? It has been suggested that, because his father was closely connected with the management of the cathedral, Filippo had known of the problem of the dome since 1402, making his first designs as early as 1409. In the intervening years he had studied classical architecture in Rome, developing his own theory of architecture from about 1410. When his model of the dome was accepted in 1418, Brunelleschi returned to Rome to investigate ancient structures, including the Pantheon. Back in Florence a year later, he built a smaller version of the dome in the Ridolfi chapel in San Jacopo sopr’Arno (since destroyed), perhaps to convince his doubters, perhaps himself. He would repeat the process six years later in a chapel built for Bartolommeo Barbardori in the church of Santa Felicita. Also in 1419, Filippo reluctantly accepted the appointment of his old rival, the sculptor Lorenzo Ghiberti, as coarchitect of the dome. Work began in 1420, and the project occupied Filippo for the rest of his life. Ghiberti’s incompetence was soon exposed (not without Brunelleschi’s connivance), and in 1423 Filippo was given complete charge.

Besides his genius for design, his success was ensured by his management of the construction site. He personally undertook the quality control of materials; he designed the plant needed to efficiently raise those materials—all 27,000 tons (24,500 tonnes)—to the dome; he resolved industrial unrest by convincing the workers of his own capabilities; he communicated with the masons by modeling details in clay, wood, wax, and even carved turnips; he ensured good working relationships; and he increased productivity by providing “vendors of wine and bread and cooks” in the heights of the dome.
Strictly speaking, Filippo’s dome is no dome at all, but a double-shell cupola formed by completely self-supporting rings of diminished diameter, built of “herringbone” brickwork (originally stone was intended but was soon abandoned because of the weight), and stiffened by a frame of eight steeply pointed arches built on centering supported from the drum. Between these ribs, Brunelleschi and his eight assistants—the “masters of the trowel”—constructed a double vault, on which a movable light shuttering supported the brickwork during construction. The finished structure was light, strong, and extremely stable. To ensure against spreading, Brunelleschi tied the bottom of the cupola with a massive chain of ironbound oak. Several reasons may be suggested for its hybridized structure. First, Brunelleschi was, quite naturally, unable to divorce himself from medieval precedent; second, while he showed great inventiveness, he did not fully understand the structural issues involved; and therefore, third, he took measures to ensure the stability of the dome. Fourth, he may have included the ribs simply to convince his clients that it was stable. “Shrewd” is how Vasari described him.

The dome was not a Renaissance building. It did not even herald the Renaissance. It drew upon Brunelleschi’s study of ancient techniques from both East and West, principally upon the engineering practice of the Middle Ages. In ingenuity it surpassed them all. The cupola was completed in 1434. Two years later the huge lantern was placed, and the cathedral was consecrated by Pope Eugene IV on 25 March 1436. The four hemidomed tribunes were completed in 1438. The decorations to the lantern were finished by 1446, when Brunelleschi was dying, and the great copper sphere crowned it all in 1474.

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