Photos

A shot of the dome from the Vatican museum. Although Michelangelo became the chief architect in 1546, his design called for a spherical dome. At the time of his death, in 1564, only the drum “base” was completed; the dome itself was redesigned and vaulted by architect Giacomo della Porta, with the assistance of Domenico Fontana, a master engineer. The double dome is made of brick and is 138.8 feet in interior diameter, almost as large as the Pantheon, rising 394 feet above the floor. Cracks began to appear by the mid 18th century, however, so measures were taken to reinforce it. It’s described as a paraboloid dome, in that it has a vertical thrust. The egg-shape exerts less pressure.