NICHOLAS V'S DECISION TO MOVE THE PAPAL RESIDENCE TO THE VATICAN altered the city's political and cultural landscape. To reflect the new status of the Vatican palace, he enlarged and improved it to serve as his residence, an administrative center for papal business, and a reception space for visiting dignitaries. For defensive reasons he linked it to Castel Sant'Angelo with a wall called the Torrione. His successors further expanded the grounds to include the heights of the Vatican Hill, where Innocent VIII Cibò (1484–1492) later built a small villa, the Belvedere. Julius II linked the palace to the villa with two long wings around a central courtyard designed by Bramante, called the Cortile del Belvedere. Sixtus V divided this in half to house the Sistine Chapel and the Salone Sistina (Fig. 183).

Nicholas V's ministrations to Rome ensured that a citywide surge in palace and church construction would ensue. In fact, the boom lasted 200 years, until the mid-seventeenth century. Colossal palaces such as the Cancelleria and the Palazzo Farnese went up with remarkable speed in the abitato. In the Borgo, too, more important prelates, nobles, and cardinals erected palaces of varying grandeur to be near the center of papal power. For example, Via Alessandrina built by Alexander VI passed alongside one flank of Piazza Scossacavalli, where, with financial inducements to develop the area, two cardinals and a papal chamberlain had all built impressive palaces by about 1520 (Fig. 184). Additionally, Rome's elite undertook to acquire large vineyards and orchards on the intramural hills – but not for their agricultural assets. From the late sixteenth century these productive slopes, favored at last with aqueduct water, were repurposed into luscious villa gardens. The horti of antiquity had returned with a vengeance.

Christendom's most important church was now more than 1,100 years old and probably in physical distress; Nicholas V proposed to demolish it and to build an entirely new basilica. But only in 1505 did Julius II authorize a design competition for a new St. Peter's, which would gradually, after many fits and starts, grow up around its Constantinian ancestor and then, inevitably, consume it.