It was begun by Caligula on the property of his mother Agrippina on the Ager Vaticanus (today's rione of Borgo), and finished by Nero. The circus building's alignment is on the same axis as both new and old St Peter's to the left as you look at the western front from the piazza.
Nearby Roman cemetery
The Via Cornelia ran parallel with the north side of the Circus, and its course can be traced with precision, for pagan tombs have been discovered at various times along its edges. Sante Bartoli's memoirs record that when Alexander VII was building the left wing of Bernini's colonnade and the lefthand fountain, a tomb was discovered with a bas-relief above the door representing a marriage-scene ("vi era un bellissimo bassorilievo di un matrimonio antico"). Others were soon found. The best discovery, that of pagan tombs exactly on the line of St Peter's tomb, was made in the presence of Grimaldi, 9 November 1616:
"On that day, I entered a square sepulchral room the ceiling of which was ornamented with designs in painted stucco. There was a medallion in the centre, with a figure in high relief. The door opened on the Via Cornelia, which was on the same level. This tomb is located under the seventh step in front of the middle door of the church. I am told that the sarcophagus now used as a fountain, in the court of......