Construction of the basilica, built over the historical site of the Circus of Nero, began during the reign of Roman Emperor Constantine I.

Over the next twelve centuries, the church gradually gained importance, eventually becoming a major place of pilgrimage in Rome.

Two people involved in this reconstruction were Leon Battista Alberti and Bernardo Rossellino, who improved the apse and partially added a multi-story benediction loggia to the atrium façade, on which construction continued intermittently until the new basilica was begun.

The whole stretch of wall has been pierced by too many openings and built too high... As a result, the continual force of the wind has already displaced the wall more than six feet (1.8 m) from the vertical; I have no doubt that eventually some... slight movement will make it collapse...[8]At first, Pope Julius II had every intention of preserving the old building, but his attention soon turned toward tearing it down and building a new structure.

[12] Constantine took great pains to build the basilica on the site he and Pope Sylvester I believed to be Saint Peter's grave, which had been marked since at least the second century.

[1] Notably, since the site was outside the boundaries of the ancient city, the apse with the altar was located in the west, so that the basilica's façade could be approached from Rome itself to the east.

When Gian Lorenzo Bernini built his baldacchino to cover the new St. Peter's altar, he drew from the twisted design of the old columns.

This giant mosaic, commissioned by Cardinal Jacopo Stefaneschi, occupied the whole wall above the entrance arcade facing the courtyard.

The nave ended with an arch, which held a mosaic of Constantine and Saint Peter, who presented a model of the church to Christ.

With its increasing prestige, the church became richly decorated with statues, furnishings and elaborate chandeliers, and side tombs and altars were continuously added.

[17] Along with the repeated translations from the ancient Catacombs of Rome and two 14th century fires in the Archbasilica of Saint John Lateran, the rebuilding of St. Peter's is responsible for the destruction of approximately half of all papal tombs.

As a result, Donato Bramante, the chief architect of modern St. Peter's Basilica, has been remembered as Maestro Ruinante.