St. Peter's Basilica
Old St. Peter's Basilica was the building that stood, from the 4th to 16th centuries, where the new St. Peter's Basilica stands today in Vatican City. Construction of the basilica, built over the historical site of the Circus of Nero, began during the reign of Emperor Constantine I. The name "old St. Peter's Basilica" has been used since the construction of the current basilica to distinguish the two buildings.