The remains of S. Sebastian were removed in the seventeenth century by Cardinal Borghesi from the crypt in which they were originally deposited and re-interred in the modern chapel which was erected over the ancient sanctuary. During the Middle Ages, when owing to the raids of the barbarians and consequent translation of the more celebrated martyrs to churches within the city, the eventful story of the catacombs was forgotten, this cemetery, owing to its connection with the two great apostles, was ever a hallowed sanctuary, and was visited by an unbroken stream of pilgrim visitors, and after the rediscovery of the City of the Dead in the sixteenth and seventeenth centuries, gave the name of its now famous district “ad Catacombas” to the various subterranean cemeteries which from time to time since then have been discovered. The corridors with their graves in this famous cemetery have not yet been fully excavated. _The Cemetery of S. Callistus._--The great group of catacombs generally known under the title “S. Callistus” is situated on the right of the Via Appia, about a quarter of a mile nearer Rome than the Cemetery of S. Sebastian (“ad Catacombas”) just described; the usual entrance being about one and a quarter miles from the Porta S. Sebastiana (Porta Appia). [Illustration: PAINTING IN A CHAPEL OF CATACOMB OF S. CALLISTUS--SHEWING A TOMB SUBSEQUENTLY EXCAVATED ABOVE THE ORIGINAL TOMB OF THE SAINT] It is composed of several groups of cemeteries of different periods from the first century to the fourth. These groups are so united by corridors that they may be considered as one vast catacomb. The Cemetery of Callistus in part dates from the first century, but it only obtained the designation of “Callistus” in the last years of the second or in the first years of the third century, when Callistus the deacon was appointed by Zephyrinus the Bishop of Rome as superintendent of _The Cemetery_. Subsequently Callistus succeeded Zephyrinus as bishop, and greatly enlarged the original area, one chamber of which he set apart as the official burying-place of the bishops or popes of Rome. Before the time of Callistus the official burying-place of the bishops was the cemetery on the Vatican Hill, immediately contiguous to the sepulchre of S. Peter. At the end of the second century the limited space on the Vatican Hill was completely occupied--hence the necessity for arranging a new papal crypt.