St. Peter's Basilica in the Vatican is the work not of a single design but of architects succeeding one another over 120 years: Bramante set up the central plan, Michelangelo designed the dome, Maderno extended the facade and the nave, and Bernini shaped the piazza and the interior. The building therefore carries in one body the transition from the pure geometry of the Renaissance to the moving, staging space of the Baroque.

The architectural heart is Michelangelo's dome. He reworks Brunelleschi's Florentine idea of the double shell at a stone scale: two separate shells, inner and outer, with a gap between them through which stairs run. The dome sits on a tall drum pierced with windows; on the outside, prominent stone ribs gather the dome's load to the drum and from there to four giant piers. The panels between the ribs are stretched between these lines.

The horizontal thrust the stone dome produces is met by iron tension chains wrapped around its base — when cracks appeared in the dome in the 18th century, these chains were multiplied to secure the structure. With an interior diameter of about 42 metres, the dome continues the Pantheon-and-Florence tradition but carries it to a higher, more vertical silhouette. St. Peter's thus sums up the Renaissance achievement in stone-dome engineering and binds it to the monumental stage of the Baroque.