St. Peter's Basilica
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Location: Vatican City, Italy
Completion Date: 1626
Diameter: 138 feet
Architect: Donato Bramante, Michelangelo
By 1506, St. Peter's Basilica, the main church at the Vatican, was too small and decrepit to impress anyone. Following the examples set by emperors and sultans, Pope Julius II decided to crown the old church with a dome. He hired Italian architect Donato Bramante to do the job. Bramante's vision for the Basilica was simple: a Greek cross with equal-sized arms around a central dome. But Bramante and the Pope died before much could be built. In 1546, a young artist from Florence named Michelangelo gained total control of the construction of St. Peter's, the largest church in Christendom.
Michelangelo designed a dome that would actually dwarf the nearby Pantheon. It would be smaller than the Pantheon in diameter, but stand much, much higher. Made almost entirely of heavy masonry, the dome stretches 138 feet in diameter and rises 452 feet above the street. To support such a giant dome, builders placed three iron rings within the masonry of the dome. But even the rings couldn't hold back the outward thrust of tension; significant cracks eventually developed around the dome's base. By the early 18th century, the cracks became serious enough for Vatican engineers to add several more tension rings as an emergency fix. Fortunately, this solution has stood the test of time.Here's how this dome stacks up against some of the biggest domes in the world.
(diameter, in feet)