3. The (so-called) _Liber Pontificalis_--a generally reliable and most interesting work, the earlier portion of which has been largely used throughout Western Christendom, certainly since the sixth century. The first part of this work contains biographical notices of the Bishops of Rome from the days of S. Peter to the times of Pope Nicholas, A.D. 807. The earliest redaction of the first Papal notices in the _Liber Pontificalis_ which has come down to us was made towards the end of the fifth century, or in the first years of the sixth. But it is evidently based on records of a much older date preserved in the Roman Church. 4. But what De Rossi found most valuable for the purposes of his great work was a group of writings known as _Itineraries of Pilgrims_. These were founded on handbooks composed for the use of devout pilgrims from Britain, Gaul, Spain, Germany, and Switzerland,--men and women who were desirous to see and to pay their devotions at the celebrated shrines of Rome. Some five at least of these precious Pilgrim Itineraries or Guide-Books to the more celebrated shrines or places where martyrs were interred in the vast Roman City of the Dead have come down to us. They have proved of the highest value to De Rossi in his exploration work. The first perhaps in value of these is contained in the works of William of Malmesbury, which treat of the doings of the Crusaders in Rome. William of Malmesbury wrote in the year of grace 1095. But the Itinerary section in question speaks of the martyr saints as though they were _still resting_ in their Catacomb graves, although we know that they had been translated into churches in the city about three centuries earlier. This clearly shows that the “Itinerary” section had been written several centuries before the writer William of Malmesbury lived and copied it into his work. Other Pilgrim Itineraries have been found in famous monastic libraries, such as in the libraries of Einsiedeln and Salzburg. These may be roughly dated about the middle of the seventh century,--that is, before the days of the Pontificate of Paul I, A.D. 757, and Paschal I, A.D. 817, when the wholesale translation of the remains of the martyrs from the Catacombs to the securer shelter of the city churches took place. These were therefore written in a period when the traditions connected with the historic crypts and their venerated contents were all comparatively fresh and vivid.