Below St. Peter’s Basilica in Rome is the Necropolis of the Vatican. Under Pope Pius XII, the original tomb of St. Peter was discovered and the necropolis excavated. Burial places of many more saints were discovered.
Necropolis of Saint Peter’s Basilica Rome
Address, Opening Hours and Admission
To enter here, you must make a reservation in advance at the Ufficio Scavi (Tel. +39 0669885318 or scavi@fsp.va) through the archway on the left side of the steps of the basilica. No more than 200 visitors are allowed in per day, in groups of 12 to 15 people, who must not be younger than 15. You will have to give your name, the period you will be in Rome and the language you speak. You will then be informed by phone or email of the date and time of your visit. You must be dressed appropriately. Taking pictures is strictly forbidden. A guide will show you the tombs excavated in the 1940s. For more information: http://www.vatican.va.
History Necropolis St. Peter’s Basilica Rome

Apart from the tomb of St. Peter himself, located directly below the papal altar, there are other burial places of saints from the first three centuries of our era here.
Saint Peter is buried on what is called field P by the archaeologists who conducted the excavations (scavi).
The excavations were carried out around the year 1940. In addition to the tomb of St. Peter, several mausoleums were found that date back to the 2nd century B.C. and were therefore of pagan origin. These are richly decorated with frescoes and other adornments.
The Christian tombs added here later are generally scarcely decorated.
According to tradition, the spot where the tomb of St. Peter is located is indicated by an aedicula called the Trofeo di Gaia.