During Nero’s great Christian persecution in 64 A.D., Saint Peter was martyred, crucified and buried in Caligula’s Circus, as one reads in the Liber Pontificalis (I, 118), “via Aurelia (…) iuxta palatium Neronianum, in Vaticanum” (In the Vatican, in Via Aurelia opposite Nero’s Palace). Eusebius of Caesarea (4th century) quotes a letter written by Gaius to Proclus, in which the presbyter invites his friend to Rome, claiming, “in the Vatican and in Via Ostiense, you will find the trophies of those who founded this Church.” For this reason, the 2nd century aedicule which was intended to protect Saint Peter’s shrine, and which was discovered during the excavations in the Vatican necropolis, was called “Gaius’s Trophy”. After Constantine’s Edict of Milan (313 A.D.) Christians were allowed to construct places of worship. Constantine himself authorized the building of the basilica in 324. It was intended to enclose “Gaius’s Trophy” and to allow Peter’s tomb to become the centre of the structure. Consecrated in 329, the great basilica appeared as a longitudinal building with a nave, four aisles and a transept. Outside, a staircase led to the four-sided portico in front of the basilica, known also as Paradise, with a fountain in the middle for the ablutions of the catechumens. Charlemagne, king of the Franks, was crowned emperor of the Holy Roman Empire in this basilica on Christmas eve in the year 800. Pilgrims gathered in the basilica from the early 14th century, having travelled on foot from all over Europe to reverence the tomb of the “Prince of the Apostles”.
When the Popes abandoned Rome during the Avignon schism (1309-1377), the basilica, which was one thousand years old by then, was showing signs of wear and deterioration. Although we have little information about these problems, we know for a fact that in the mid 15th century, Pope Nicholas V asked the architect Bernardo Rossellino to draw up a project for a new choir, outside the Constantinian apse. It was built to a height of about 1.5 metres.
By the early 16th century, the need to choose between restoring St Peter’s or rebuilding it completely was unavoidable, so much so that the new Pope Julius II, elected in October 1503, decided to entrust this task to Donato Bramante in 1505, one of the greatest architects of his time.