Michelangelo's interest in architecture developed from designing complex monumental sculptural ensembles within a coherent architectonic framework. Indeed, the concept of architecture as a grid intended to set off sculpture, as in the Julius tomb, links all his early architectural designs.
The New Sacristy (1519-33) of San Lorenzo, Florence, and the Biblioteca Laurenziana (begun c. 1524) were singled out by Vasari as marking a conscious break with ancient and modern tradition in their use of licentious non-Vitruvian detail. During the short-lived Republican government of 1527-30, Michelangelo was ready to harness his design skills to modernizing the city's medieval defences. In April 1529 he was appointed governor general of the city's fortifications, and supervised the construction of bastions and bulwarks.
Michelangelo moved permanently to Rome in 1534. Here two popes in particular - Paul III and Pius IV - had the imagination to entrust him with architectural projects of the greatest importance. Redesigning the Piazza del Campidoglio on the Capitoline Hill was one of Michelangelo's most successful architectural achievements and one of the most perfectly realized examples of Renaissance urban planning. His work at St Peter's is unquestionably the crowning achievement of his architectural career. The Piazza del Campidoglio and the dome of St. Peter's are still among the city's most notable visual images. He did not finish either, but after his death both were continued in ways that probably did not depart much from his plans.