The _Fourth Book_ is devoted exclusively to the story of the Roman Catacombs. In the course of the second half of the nineteenth century, the vast subterranean City of the Dead, known as the Roman Catacombs, has been in parts patiently excavated, and carefully studied by eminent scholars. This study, which is still being actively pursued, has thrown much light upon the “life” lived among the early generations of Christians. The inscriptions and epitaphs graved and painted, the various symbols carved upon the countless tombs in the Catacombs, have told us very much of the relations between the rich and the poor. They have disclosed to us something of the secret of the intense faith of these early believers on the “Name,” and have shown us what was the sure and certain hope which inspired their wonderful endurance of pain and agony, and their marvellous courage in the hour of trial. All this and much more the inscriptions on the thousand thousand graves, the dim fading pictures, the rough carvings, speak of in a language none can mistake. It is, indeed, a voice from the dead, bearing its strange, weird testimony which none can gainsay or doubt. The work of excavation and the patient study of these Catacombs are yet slowly proceeding, but from what has been already discovered we have learned much of the “Inner Life” of this early Christian folk. The history of these wonderful Catacombs, this subterranean city of the dead beneath the suburbs of ancient Rome, is told at some length and with considerable detail in the Fourth Book. The _Fifth Book_ may be considered as a supplement to the work, which in the first four Books has dwelt on (1) the very early history, and (2) on the “Inner Life” of the Christian Church in the first three centuries, especially in Rome. Christianity sprang from the heart of the Chosen People, the Jews. The Divine Founder in His earthly life was pleased to be a Son of the Chosen People, and His disciples, who laid the early stories of the Faith, were all Jews, as were the earliest converts to the religion of Jesus. The history of the Jews--their past and present condition--is indissolubly bound up with the records of Christianity. It constitutes the most important confirmation which we possess of the truth of early Christian history. It is the weightiest of all evidential arguments here, and it cannot be refuted or disproved. The general account of the Chosen People before the coming of Messiah is well known, and the historical accuracy of the Old Testament records is generally admitted. But the memories of the fortunes of the Jewish race after A.D. 70, when the Temple and City were destroyed, and when the heart of Judaism, as it were, ceased to beat, are comparatively little known.