It might very well happen that some members of the family were Christians and others were not, and this would account for the mixture of Pagan tombs with Christian ones in the same catacombs. The subterranean sand-pit roads frequently run parallel to the high roads at a little distance from them, and such a road passing at the back of the subterranean cemetery or catacomb would be very convenient to Christians in time of persecution. The part of these roads which came within the limits of the cemetery would naturally be used for burial places, also, as we see that they were distinctly in the case of S. Hermes, and nearly with equal certainty in other cases. In ordinary times, there was no necessity for secrecy. The bodies of Christian martyrs were given up for the purpose of burial to those who applied for them.
The catacombs of SS. Saturnius and Thraso, the entrance to which is in the gardens of the Villa Gangalani, about a mile from Rome, on the Via Salaria, are stated to have formed part of the great catacomb of S. Priscilla, the entrance to which is about a quarter of a mile farther from Rome, on the same road. On descending into that of S. Saturninus by a steep flight of steps of modern appearance, but perhaps restored only, we soon pass under the road and hear carriages passing overhead; we then continue to descend to the depth of about fifty feet, divided into five corridors, only four of which can at present be seen; but we pass the entrance to the fifth on one of the stair-cases, and see the opening to it. The two lower corridors of this catacomb have tombs or cubicula on the sides; a few of these are painted, and the vault of the corridor in front of them, also.
The sandstone in which this catacomb is made is more than usually hard, for which reason apparently there are only three of the side chapels for family burying places, and few of the arched tombs; most of the recesses for graves are merely parallelograms just large enough to contain the body, or two bodies side by side, one behind the other, the recess being excavated to a sufficient depth for that purpose, and some of these have the slabs covering the openings left in their places. The skeletons are allowed to remain in several of the tombs where the slab has been removed and left open. One of the chapels has remains of paintings of the fourth century in a very decayed state. The other two chapels are connected by a short passage; they have evidently been family burying places, a second added when the first was full. The passage is made through the principal tomb of the first chapel, the body previously interred there was probably removed to the inner chapel when that was made. The painted chapel is in the upper corridor, the double one in the lowest.
In descending from the garden, the two upper corridors have tombs on the sides, and are regular catacombs; the third is an arenarium, or sand-pit, without tombs, and large enough for a horse and cart to pass along, as in the ordinary sand-pits. There must have been another entrance to this, and it is said to have been half a mile off, which is not improbable, judging by other sand-pits, both those now in use and others that are closed, some of which are known to be more than a mile long, and with the different branch galleries, the corridors altogether often extend several miles. These galleries are large and wide enough for a horse and cart, but not for two to pass, sidings being made at intervals for that purpose. The passages in the catacombs vary much both in height and in width, but are seldom more than three feet wide. The chapels also vary in size, but none of them would hold more than fifty people; those in the present catacomb are small.
LAMPS FOUND IN THE CATACOMBS.[ToList]
That each of these chapels was the burial-place of a family, and was considered as private property, is evident from the remains of a door at the entrance of several of them, as in the catacomb of S. Priscilla. In one of these, the stone corbel, with the hole for the pivot to work in, remains in its place; the lower stone, with the corresponding hole, has been moved, but is lying on the floor in an adjoining chapel. Another door has been made to slide up and down like a portcullis or a modern sash-window, as we see by the groove remaining on both sides. This is close to a luminaria, or well for admitting light and air, and it seems quite possible that it really was a window, or that the upper part was made to slide down to admit the light and air from the luminaria. If this was the burial-place of Priscilla, the paintings were probably renewed in the restoration by John I., A.D. 523. The lower part of the wall is faced with stucco paneled with oblong panels, colored in imitation of different kinds of marble; the stucco is about an inch thick, like slabs of marble, and the divisions between the panels are sunk to that depth, as if each panel had been painted before it was placed and fixed to the walls like marble slabs. There are some long narrow slips of white stucco lying about, which seem to have been fitted into the hollow grooves between the slabs. The vaults in this catacomb are in many parts supported by brick arches; in one place, at a crossing, are four small low brick arches, the character of which agrees with the period of the restoration in the sixth century; the mortar between the bricks or tiles is about the same thickness as the tiles themselves, which are rather more than an inch thick, so that there are five tiles to a foot, including the mortar between them. These brick arches are not subsequent repairs, but part of the original construction to carry the vault. The arenarium, or sand-pit gallery, through which the present entrance is made, has evidently been used as a subterranean road. A branch of an aqueduct running along the side of this is part of an extensive system of irrigation carried on throughout all this district, the water having been brought from the Aqua Virgo, which passed in this direction. It was probably part of the original line of the Aqueduct, which has been altered in the portion near to Rome; this has not been traced out to any considerable extent, but Signor de Rossi has found many remains and indications of it. The sand-pit roads, or arenaria, ran for miles parallel to the high roads, and were probably used by the carters in preference to the open roads in hot weather, as they are always cool.
Christian Inscriptions are all funereal, and are for the most part found in the catacombs, or subterranean cemeteries. The word cemetery is derived from a Greek word, meaning "a sleeping place," hence the frequent formulæ in the Christian epitaphs, "dormit in pace," he sleeps in peace; "dormitio Elpidis," the sleeping place of Elpis; "cubiculum Aureliæ," the sleeping chamber of Aurelia. The term catacomb was applied to these subterranean cemeteries at a much later period. The practice of subterranean burial among the early Christians was evidently derived from the Jewish custom of burying the dead in excavated sepulchres, and thus may have been adopted by the early Jewish converts. The Roman Jews had a very early catacomb of their own, in the Monte Verde, contiguous to their place of abode, in the Trasteverine quarter of Rome. This subterranean mode of sepulture is undoubtedly of Egyptian origin. It is generally supposed that the early Christians used for their burial places the excavations made by the Romans for procuring stone and cement for building purposes. This is an erroneous view. Recent geological observations on the soil of the Agro Romano have shown that the surface of the Campagna consists of volcanic rocks of different natures and ages. The earliest of the series, the tufa lithoide, was constantly employed from the earliest ages in the buildings of the city, as attested by the massive blocks of the Cloaca Maxima, the tabularium of the Capitol, and the walls of Romulus; the second, or tufa granolare, which though it has just consistency enough to retain the form given to it by the excavator, can not be hewn or extracted in blocks; and the pozzolana, which has been extensively used in all ages for mortar or Roman cement. The tufa lithoide and the pozzolana were thus alone used for building purposes by the Romans, and the catacombs are never found excavated in these. The catacombs were hewn only in the tufa granolare, and were consequently excavated expressly for burials by the early Christians. The Christian architects carefully avoided the massive strata of the tufa lithoide, and we believe it is ascertained that all the known catacombs are driven exclusively along the courses of the tufa granolare. With equal care these subterranean engineers avoided the layers of pozzolana, which would have rendered their work insecure, and in which no permanent rock tomb could have been constructed. Thus we arrive at the curious fact, that in making the catacombs the excavators carefully avoided the strata of hard stone and the strata of soft stone, used respectively for building and for mortar, and selected that course of medium hardness which was best adapted to their peculiar purpose. The early Christian tomb inscriptions are characterized by symbols and formulæ peculiar to the Christian creed; the idea of another life, a life beyond the grave, usually prevails in them.