Inside the Catacombs of San Sebastiano, four levels have been excavated. Near the catacombs, the Appian Way passes through a valley. On its slopes houses and columbarii were built. In the valley bottom (called "ad catacumbas" now synonymous with underground cemetery) were erected three mausoleums which probably marked the beginning of the cemetery. When the Church became the owner of the site in the 3rd century the mausoleums were covered by a platform arranged as a covered courtyard called a triclia. In the 4th century a basilica with a nave and two aisles was built above the earlier structures and surrounded by mausoleums. It was here, near where the Apostles Peter and Paul were venerated, that St Sebastian was buried. He was a soldier martyred during the persecution in Diocletian’s reign (284-305). When he was finally discovered to be a Christian, in 286, he was handed over to the Mauretanian archers, who pierced him with arrows; he was finally killed by the blows of a club and his body was thrown into the Cloaca Maxima. He miraculously appeared to the matron Irene who collected his body and carried to the catacombs that bear his name. His cult became so popular that in the 5th century a crypt was excavated around his tomb. The basilica was altered in the 13th century then rebuilt in the 17th century for Cardinal Scipio Borghese. The new church was built above the nave of the previous building.

The tour of this catacomb, which has second-century pagan tombs along with Christian chapels, will take you down a staircase studded with pieces of sarcophagi with imperial seals. Underneath the church, you’ll see an area with three decorated pagan tombs with some very attractive frescoes and a floor mosaic. It is believed that both Christian and pagan funerals were held in the elaborate central chapel, the vault of which has acanthus and lotus-leaf stucco decorations. The Chapel of Symbols has early Christian symbols carved in it. Up another staircase is a dining room for funeral banquets. The graffiti date back to the second century.