The tomb of the Caetennii (17 x 18 feet) was one of the richest and most lavishly decorated of all those excavated beneath St. Peter's.
Workmen examining underneath the floor of Basilico.
Pope Pius XI, whose desire to be buried below St. Peter's nave led to the historic excavations, lies in his stone sarcophagus in renovated upper grottoes.
The interior of St. Peter's basilica, with markers indicating the location of the excavation beneath the floor, 1950.
LIFE examines the history beneath St. Peter's Basilica at the Vatican. For more photos, click here.