<P> The Vatican Necropolis lies under the Vatican City, at depths varying between 5--12 meters below Saint Peter's Basilica . The Vatican sponsored archeological excavations (also known by their Italian name scavi) under Saint Peter's in the years 1940--1949 which revealed parts of a necropolis dating to Imperial times . The work was undertaken at the request of Pope Pius XI who wished to be buried as close as possible to Peter the Apostle . It is also home to the Tomb of the Julii, which has been dated to the third or fourth century . The necropolis was not originally one of the underground Catacombs of Rome, but an open air cemetery with tombs and mausolea . </P> <P> The Vatican Necropolis is not to be confused with the Vatican grottoes, the latter of which resulted from the construction of St. Peter's Church and is located on the ground level of the old Constantinian basilica . </P>

What is the vatican built on top of