In 1939, in the reign of Pope Pius XII, 10 years of archaeological research began, under the crypt of the basilica, an area inaccessible since the 9th century. The excavations revealed the remains of shrines of different periods at different levels, from Clement VIII (1594) to Callixtus II (1123) and Gregory I (590–604), built over an aedicula containing fragments of bones that were folded in a tissue with gold decorations, tinted with the precious murex purple. Although it could not be determined with certainty that the bones were those of Peter, the rare vestments suggested a burial of great importance. On 23 December 1950, in his pre-Christmas radio broadcast to the world, Pope Pius XII announced the discovery of Saint Peter's tomb.

Saint Peter’s Basilica can host 20,000 people. It is 190 m long, the aisles are 58 m wide, the nave is 45.50 m high as far as the vault, the dome is about 136 m high as far as the cross.