The earliest certain traces of special buildings for divine worship which had been held previously in private houses of Christians are met with in Tertullian about the end of the 2nd century. In Diocletian’s time Nicomedia became a royal residence and hard by the emperor’s palace a beautiful church proudly reared its head (§ 22, 6), and even in the beginning of the 3rd century Rome had forty churches. We know little about the form and arrangement of these churches. Tertullian and Cyprian speak of an altar or table for the preparation of the Lord’s supper and a desk for the reading, and in the _Apostolic Constitutions_ it is required that the building should be oblong in shape. The wide-spread tradition that in times of sore persecution the worshippers betook themselves to the Catacombs is evidently inconsistent with the limited space which these afforded. On the other hand, the painter whose works, by a decree of a Spanish Council in A.D. 306, were banished from the churches, found here a suitable place for the practice of sacred art. § 38.1. =The Catacombs.=--The Christian burying places were generally called κοιμητήρια, _Dormitoria_. They were laid out sometimes in the open fields (_Areæ_), sometimes, where the district was suitable for that, hewn out in the rock (κρύπται, crypts). This latter term was, by the middle of the 4th century, quite interchangeable with the name _Catacumbæ_, (κατὰ κύμβας=in the caves). The custom of laying the dead in natural or rock-hewn caves was familiar to pagan antiquity, especially in the East. But the recesses used for this purpose were only private or family vaults. Their growth into catacombs or subterranean necropolises for larger companies bound together by their one religion without distinctions of rank (Gal. iii. 28), first arose on Christian soil from a consciousness that their fellowship transcended death and the grave. For the accomplishment of this difficult and costly undertaking, Christian burial societies were formed after the pattern of similar institutions of paganism (§ 17, 3). Specially numerous and extensive necropolises have been found laid out in the immediate neighbourhood of Rome. But also in Malta, in Naples, Syracuse, Palermo, and other cities, this mode of sepulchre found favour. The Roman catacombs, of which in the hilly district round about the eternal city fifty-eight have been counted in fourteen different highways, are almost all laid out in the white porous tufa stone which is there so abundant, and useful neither for building nor for mortar. It is thus apparent that these are neither wrought-out quarries nor gravel pits (_Arenariæ_), but were set in order from the first as cemeteries. A few _Arenariæ_ may indeed have been used as catacombs, but then the sides with the burial niches consist of regularly built walls. The Roman Catacombs in the tufa stone form labyrinthine, twisting, steep