Comparing the various Pilgrim Guides together, De Rossi found that, with very minor differences in the details, they agreed wonderfully; and in the main, although composed a thousand to thirteen hundred years ago, he was able with their help to identify the principal shrines visited by the pilgrim crowds of the sixth and two following centuries. (1) _The Cemetery of S. Sebastian_ (“_ad Catacombas_”) is situated on the Via Appia, right-hand side; about one and a half miles from the Porta S. Sebastiana (the ancient Porta Appia). The principal “memory” belonging to this catacomb is the Platonia chamber--so called from its having been lined with marble--in which for a brief season were deposited the bodies of the two Apostles SS. Peter and Paul. The fact of this chamber having been the temporary home of the sacred bodies is undisputed; the exact date of their having been placed there, and the length of the period during which they were left in the Platonia chamber in question, have been the subject of much controversy. The period of forty years mentioned in the above-quoted Pilgrim Itinerary is now reduced by the most dependable of modern scholars to two years, and the date of the placing of the bodies in this spot is now generally assumed to have been A.D. 258, in the days of the short but bitter persecution of Valerian, when the tombs on the Vatican Hill and on the Via Ostiensis were not considered safe from outrage. When the active persecution ceased, the remains of the two apostles were restored to their original resting-places; the spot, however, where the sacred bodies had rested for a brief season assumed in the eyes of the faithful a singular sanctity, and very many desired to be laid in the immediate neighbourhood of the hallowed place. This was no doubt the original reason for the formation of the Cemetery “ad Catacombas,” the name of the little district in which the temporary tomb of the two apostles was situated. The catacomb in question was eventually named after Sebastian, a brave confessor in the persecution of Diocletian, _circa_ A.D. 289-303. This Sebastian was tribune in the first cohort and commanded a company of the Prætorians, which was stationed on guard on the Palatine. He died for his faith under circumstances of a peculiar dramatic interest, being pierced with arrows and cruelly scourged. His body, so runs the probably true story, was taken out of the common sewer, into which it was ignominiously thrown, by a Christian matron named Lucina, who reverently interred it in the Cemetery “ad Catacombas” in the neighbourhood of the sacred Platonia chamber.