Michelangelo's Dome
Michelangelo's Dome of Basilica di San Pietro. The dome, or the cupola, was designed by Michelangelo, who became chief architect in 1546. At the time of his death (1564), the dome was finished as far as the drum, the base on which a dome sits. The dome was vaulted between 1585 and 1590 by the architect Giacomo della Porta with the assistance of Domenico Fontana, who was probably the best engineer of the day. Fontana built the lantern the following year, and the ball was placed in 1593.
As built, the double dome is brick, 42.3 metres (138.8 ft) in interior diameter (almost as large as the Pantheon), rising to 120 metres (394 ft) above the floor. In the mid-18th century, cracks appeared in the dome, so four iron chains were installed between the two shells to bind it, like the rings that keep a barrel from bursting. (Visitors who climb the spiral stairs between the dome shells can glimpse them.) The four piers of the crossing that support it are each 18 metres (59 ft) across. It is not simply its vast scale (136.57 m or 448.06 ft) from the floor of the church to the top of the added cross) that makes it extraordinary.
Michelangelo's dome is not a hemisphere, but a paraboloid: it has a vertical thrust, which is made more emphatic by the bold ribbing that springs from the paired Corinthian columns, which appear to be part of the drum, but which stand away from it like buttresses, to absorb the outward thrust of the dome's weight. The grand arched openings just visible in the illustration but normally invisible to viewers below, enable access (but not to the public) all around the base of the drum; they are dwarfed by the monumental scale of their surroundings. Above, the vaulted dome rises to Fontana's two-stage lantern, capped with a spire.
Other domes around the world, built since, are always compared to this one which served as model: Saint Joseph's Oratory in Montreal, Quebec, St Paul's Cathedral in London, Les Invalides in Paris, United States Capitol in Washington, DC, the Pennsylvania State Capitol in Harrisburg, Pennsylvania, Missouri State Capitol in Jefferson City, Missouri, the Texas Capitol in Austin, Texas,and the more.
