by law and was untouchable. However, Emperor Constantine I decided to build a basilica, which would be located just above the supposed grave of the Apostle Peter. To obtain the necessary amount of flat area for the planned construction, Emperor Constantine I excavated part of the necropolis of the Vatican hill, which can be seen in the figure. This caused the necropolis to be filled with soil and building debris, with the exception of St. Peter's tomb, which was preserved. Excavations 20th century The first excavations of the Necropolis occurred from 1940–1949 during the pontificate of Pius XII. The purpose of these excavations was to locate the grave of St. Peter, which for centuries had been assumed to be beneath St. Peter's Basilica. A series of mausoleums were unearthed. The mausoleums were initially labeled with the Greek alphabet letters Φ (phi), Χ (chi) and Ψ (Psi). Later, Latin letters were used. The Mausoleum M had already been described in 1574, and Mausoleum O was discovered when it was unearthed during the construction of the foundation for the statue of Pope Pius VI. Mausoleums R and S were discovered when the southern part of the foundation for the canopy of Gian Lorenzo Bernini was created. First, the A mausoleum was built. In later years, in rapid succession, the mausoleums B, C, D and E were built next to each other. The Mausoleum G is very likely from the same time as Mausoleum B, while Mausoleum F was probably created during the reign of Antoninus Pius (138–161 AD). These seven mausoleums were placed in a row, built as standalone buildings with different heights and forming an approximately 32-meter-long road. In later times, the gap was filled by mausoleums G and O and with other buildings. In the reign of (Emperor) Hadrian, Mausoleum O was built. Only Mausoleum H, from the second half of the 2nd Century, deviates from the straight row because of a pre-built Atrium. By this time the Circus was no longer in use; thus, it was no longer an obstacle to the spread of the necropolis to the south. The Circus at the time was already overbuilt with various tombs. A grave from the same time as the construction of Mausoleum H was found near the foundation of the obelisk. When the Circus was eventually razed, to the already existing series of mausoleums was built another group, namely the