To enable the reader fairly to grasp something of the vast extent, the nature, and importance of these Catacombs of Rome, whose silent witness to the “Inner Life” of the early Church is invoked, this Fourth Book will give: (1) a brief description of the way in which the investigations into this wonderful “City of the Dead” in later years has been carried out by careful scholars and experts; (2) a general and somewhat detailed account of the situation and features of the several Catacombs, dwelling especially on the more important of these cemeteries; (3) the teaching contained in the inscriptions, carvings, and paintings on the graves in the Catacomb corridors. PART I I Since the date of what may be termed the rediscovery of the Catacombs in the vineyard on the Via Salaria in 1578[120] the work of excavation and research in the streets of the City of the Dead which lies beneath the suburbs of Rome has been slowly and somewhat fitfully carried on, exciting generally but little public interest, and until the last fifty years, roughly speaking, has been most mischievous and destructive. It is probable that more destruction and havoc have been wrought by the well-meaning but ill-directed efforts of the explorer than were occasioned by the raids of the barbarians in the sixth and two following centuries and by the slow wear and sap of time. Among these, Bosio, A.D. 1593-1629, the pioneer of the Catacomb explorers, occupies one of the few honourable places; his method of working was in many respects scientific. He was no mere explorer, working haphazard, but he guided his labours by carefully sifting all the information he could procure of the past history of the vast subterranean necropolis. But, after all, the materials of this history which he could get together were scanty when compared with the materials possessed by scholars of our day and time, and in consequence many of the conclusions to which this pioneer of Catacomb research came to were erroneous. But in his manner of working Bosio had no successors. As a rule, since that really illustrious scholar and searcher has passed away, alas! a very different method has been with rare exceptions followed by explorers of the Catacombs, and owing to the careless and ill-regulated excavations which have been fitfully carried on during some 200 and more years, irreparable damage has been done, and the losses to this deeply important branch of early Christian history are simply incalculable. The general results of this unfortunate exploration work in the past have been summarised as follows: