The Vatican necropolis lies beneath Vatican City, at a depth ranging from 5 to 12 meters below the present St. Peter's Basilica. In the 1940s, the Holy See sponsored archaeological excavations in the area, revealing a necropolis dating back to imperial times. This project was promoted by Pope Pius XI, who wished to be buried as close to St. Peter's as possible. Among the discoveries was the Tomb of the Julii, dating from the 3rd or 4th centuries. The necropolis should not be confused with the subway catacombs of Rome, as it was an open-air cemetery with tombs and mausoleums.

Unlike the Vatican grottoes, which arose with the construction of the present St. Peter's Basilica and correspond to the lower level of the ancient Constantinian basilica, the necropolis was originally a cemetery on the southern slope of the Vatican Hill, next to a circus built by the emperor Caligula. According to Roman law, it was forbidden to bury the dead within the city walls, so cemeteries were located along roads outside the city limits. From Rome, access was via the Via Cornelia, which ran northward along the Vatican Hill.

Caligula, during the construction of the circus later completed by Nero, placed an Egyptian obelisk, which remained in its original location until Domenico Fontana moved it to the center of St. Peter's Square in 1586 on the orders of Pope Sixtus V.

According to tradition, St. Peter was martyred around 64 or 67 in Nero's Circus and buried in the adjacent necropolis. After the Edict of Milan, Emperor Constantine I began construction of the first Vatican basilica. Although the necropolis was still in use, Constantine ordered to excavate part of it to level the ground and build the foundations of the church, filling it with rubble. Only the tomb of St. Peter was preserved.

The first excavations of the necropolis were carried out between 1940 and 1949, under the pontificate of Pius XII, with the aim of locating the tomb of St. Peter. During the excavations, several mausoleums were discovered, initially marked with letters of the Greek alphabet and then with Latin letters. Among the mausoleums discovered, some date back to the 2nd and 3rd century and were built during the reign of different emperors. These mausoleums were used by several generations and shared by different families.

In the 21st century, during the construction of a parking lot in 2003, another part of the necropolis was discovered. This site, now open to visitors, has seen several restorations, such as that of the Valerii Mausoleum.

Zone P, also known as Campus Petri, is the site of the supposed tomb of St. Peter. According to tradition, after his martyrdom in Nero's Circus, Peter was buried here. Approximately 100 years later, a chapel was erected over his tomb, adjacent to the so-called "red wall". This site was an early place of veneration, known as the "Trophy of Gaius" after the theologian Gaius of Rome, mentioned in the work of Eusebius of Caesarea.

Visits to the Vatican necropolis must be arranged with the Excavations Office of the Fabric of St. Peter's at least six months in advance. The visit, which lasts about an hour and a half, culminates at the tomb of St. Peter and ends in the basilica. For conservation reasons, only small groups of ten to fifteen people at a time are allowed.