San Sebastiano fuori le mura (Saint Sebastian outside the walls) was built originally in the first half of the 4th century. The basilica is dedicated to St. Sebastian, a popular Roman martyr of the 3rd century. 'Fuori le mura' refers to the fact that the church is built outside the Aurelian Walls, and is used to differentiate the basilica from the church of San Sebastiano al Palatino on the Palatine Hill.
The church is built above one of Rome's famous catacombs or underground cemeteries, and in fact the word 'catacomb' comes from this site. According to the founding tradition, in 258, during the Valerian persecutions, the catacombs were temporarily used as place of sepulture of two other saints martyred in Rome, Peter and Paul, whose remains were later transferred to the two basilicas carrying their names: whence the original dedication of the church, Basilica Apostolorum ('Basilica of the Apostles'). The dedication to Sebastian dates to the 9th century.
Sebastian's remains were moved here around 350. They were transferred to St. Peter's in 826, fearing a Saracen assault: the latter, in fact, materialized, and the church was destroyed. The building was refounded under Pope Nicholas I (858–867), while the martyr's altar was reconsecrated by Honorius III (1216–1227), by request of the Cistercians, who had received the place. In the 13th century the arcade of the triple nave was walled in.
The current edifice is largely a 17th-century construction, commissioned by Cardinal Scipione Borghese in 1609 from Flaminio Ponzio and, after Ponzio's death in 1613, entrusted to Giovanni Vasanzio, who completed it.
The statue of St Sebastian at the altar in the first chapel on the left is by Giuseppe Giorgetti. The Chapel of Relics, located directly across the nave, houses a stone allegedly imprinted with the footprints of Jesus related to the episode of 'Quo vadis?' in the apocryphal Acts of Peter; and one of the arrows which struck St Sebastian together with part of the column to which he was tied during the martyrdom. Noteworthy is the Albani Chapel (built 1716) and designed by Carlo Maratta, Alessandro Specchi, Filippo Barigioni and Carlo Fontana; commissioned by Pope Clement XI; and dedicated to Pope Fabian. Fabian had been Bishop of Rome during the persecution of Decius. Flanking the altar, busts of Saints Peter and Paul by Nicolò Cordier recall the first dedication of the basilica.
References:The Walls of Constantinople are a series of defensive stone walls that have surrounded and protected the city of Constantinople (today Istanbul) since its founding as the new capital of the Roman Empire by Constantine the Great. With numerous additions and modifications during their history, they were the last great fortification system of antiquity, and one of the most complex and elaborate systems ever built. They were also the largest and strongest fortification in both the ancient and medieval world.
Initially built by Constantine the Great, the walls surrounded the new city on all sides, protecting it against attack from both sea and land. As the city grew, the famous double line of the Theodosian Walls was built in the 5th century. Although the other sections of the walls were less elaborate, they were, when well-manned, almost impregnable for any medieval besieger.