It was designed by Michelangelo, who from 1547 dealt continuously with the Basilica. At the end of his long life (he died at 89 years of age in 1564) the construction had reached the drum, characterized by strongly protruding paired columns alternating with gabled windows.
Then the management of the factory passed to Giacomo Della Porta, a pupil of Michelangelo, who raised the vault of the dome by about 7 meters and completed the works in just 22 months, in 1590, during the pontificate of Pope Sixtus V.
With a double cap, the dome has an internal diameter of 42.56 meters and a height at the top of the cross of 136.57 meters; the lantern is 17 meters high.
It served as a model in the western world for subsequent realizations: among the many, even if built in a technically different way, the dome of San Paolo in London (1675), that of Les Invalides in Paris (1680-1691) and the neoclassical roof of the Washington Capitol (1794-1817).