In the early years of the third century--the wonderful “find” of the Papal Crypt in the Callistus Cemetery, and the ruined remains of the tombs of several of the Bishops of Rome, confessors and martyrs, bear irrefragable testimony to the truth of records of early Christian history, and set a seal upon tradition hitherto only held with but a half-hearted confidence. In the middle years of the same century the identification of the tombs of Agnes and her foster-sister Emerentiana replaced in the pages of serious history scenes often quoted in early martyrology, but which competent Christian critics had long relegated to the region of the merely legendary. The exploration and labours of De Rossi and his band of fellow-workers and pupils have also thrown a flood of light on the days of the fierce continuous persecution of the Emperor Diocletian, and have opened out to publicity a number of tombs of nameless martyrs who suffered under the iron hand of imperial Rome in the bloody times of that last and fiercest of attacks on Christianity. And besides the many nameless graves of a great multitude of martyrs and confessors who suffered under Diocletian, these explorations have identified the tombs of not a few of the more famous Christian leaders who witnessed a good confession at that same dread epoch, notably the resting-places of Peter and Marcellinus, of the Roman bishops Caius and Eusebius, of Marcus and Marcellinus. “A very glorious group of monuments--a group, too, which we may well expect to become larger and more far-reaching in its teaching, for _innumerable crypts are still waiting to be explored and searched out_. Each of the ancient roads leading from the immemorial capital of Italy, and once of the world; each historic cemetery or catacomb contains such a crypt with its central shrine of some once well-known martyr or illustrious confessor of the Name.” So writes Marucchi, one of the foremost of the living Roman scholars in Catacomb lore, the disciple and successor of De Rossi. (These words were written in the year of grace 1903.) Following closely upon the notices contained in the Pilgrim Itineraries of the seventh and eighth centuries, De Rossi, in a catalogue carefully composed, enumerates thirty-seven cemeteries or Catacombs. Several, however, of these have not been clearly identified. One or two of them are very small; while others, apparently extending over a wide area, communicate with one another; and some are very imperfectly known, others as yet quite unexplored. III It will be an assistance to the student wishing to grasp something of the vast extent of the great subterranean City of the Dead, and desirous to arrive at some idea of the present knowledge of the mighty Christian necropolis of the first days, if a brief sketch of the known cemeteries and their more important crypts is presented.