made available for the interment of the poorer members of the infant Church. In accordance with a common Roman usage the ground thus set apart for the purpose of sepulture was placed under the protection of the law, and was accurately defined, to secure it from trespass or violation. While the protection of the law was enjoyed, the excavations were strictly confined within the limits of these areas, and lower piani were dug rather than transgress the boundary. But when that protection was withdrawn the galleries were horizontally extended, often for the purpose of facilitating escape, and connections were made with adjacent areas, till the whole became an intricate labyrinth of passages and chambers. These areas are still further distinguished by certain peculiarities in the inscriptions, cubicula, and paintings, and were greatly modified by subsequent constructions.
It has till recently been thought that the Catacombs were originally excavations made by the Romans for the extraction of sand and other building material, and afterward adopted by the Christians as places of refuge, and eventually of sepulture and worship. This opinion was founded on a few misunderstood classical allusions and statements in ancient ecclesiastial writers, and on a misinterpretation of certain accidental features of the Catacombs themselves. It was held, nevertheless, by such eminent authorities as Baronius, Severano, Aringhi, Bottari, D’Agincourt, and Raoul-Rochette. Padre Marchi first rejected this theory of construction, and the brothers De Rossi have completely refuted it. An examination of the material in which these sand pits and stone quarries and the Catacombs were respectively excavated, as well as of their structural differences, will show their entirely distinct character.
The surface of the Campagna, especially of that part
occupied by the Catacombs, is almost exclusively of volcanic origin. The most ancient and lowest stratum of this igneous formation is a compact conglomerate known as tufa lithoide. It was extensively quarried for building, and the massive blocks of the Cloaca Maxima and the ancient wall of Romulus attest the durability of its character. Upon this rest stratified beds of volcanic ashes, pumice, and scoria, often consolidated with water, but of a substance much less firm than that of the tufa lithoide, and called tufa granolare. In insulated beds, rarely of considerable extent, in this latter formation, occurs another material, known as pozzolana. It consists of volcanic ashes deposited on dry land, and still existing in an unconsolidated condition. This is the material of the celebrated Roman cement, which holds together to this day the massy structures of ancient Rome. It was conveyed for building purposes as far as Constantinople, and the pier on the Tiber from which it was shipped is still called the Porto di Pozzolana. It is in these latter deposits exclusively that the arenaria, or sand pits, are found. The tufa granolare is too firm, and contains too large a proportion of earth, to use as sand, and is yet too friable for building purposes. Yet it is in this material, entirely worthless for any economic use, that the Catacombs are almost exclusively excavated; while the tufa lithoide and the pozzolana are both carefully avoided where possible, the one as too hard and the other as too soft for purposes of Christian sepulture. Sometimes, indeed, as at the cemeteries of St. Pontianus and St. Valentinus, for special reasons, Catacombs were excavated in less suitable material; but still the substance removed—a shelly marl—was economically useless, and the galleries had to be supported by solid masonry. The tufa granolare, on the
contrary, was admirably adapted for the construction of these subterranean cemeteries. It could be easily dug with a mattock, yet was firm enough to be hollowed into loculi and chambers; and its porous character made the chambers dry and wholesome for purposes of assembly, which was of the utmost importance in view of the vast number of bodies interred in these recesses.
The differences of structure between the quarries or arenaria and the Catacombs are no less striking. To this day, the vast grottoes from which the material for the building of the Coliseum was hewn, most probably by the Jewish prisoners of Titus, may still be seen on the Cœlian hill. It is said that in those gloomy vaults were kept the fierce Numidian lions and leopards whose conflicts with the Christian martyrs furnished the savage pastime of the Roman amphitheatre. But nothing can less resemble the narrow and winding passages of the Catacombs than those tremendous caverns.
Nor is there any greater resemblance in the excavations of the arenaria. These are large and lofty vaults, from sixteen to twenty feet wide, the arch of which often springs directly from the floor, so as to give the largest amount of sand with the least labour of excavation. The object was to remove as much material as possible; hence there was often only enough left to support the roof. The spacious passages of the arenaria run in curved lines, avoiding sharp angles, so as to allow the free passage of the carts which carried away the excavated sand. In the Catacombs, on the contrary, as little material as possible was removed; hence the galleries are generally not more than three, or sometimes only two, feet wide, and run for the most part in straight lines, often crossing each other at quite acute angles, so that only very narrow carts can be used in
cleaning out the accumulated débris of centuries—a very tedious process, which greatly increases the cost of exploration. The walls, moreover, are always vertical, and the roof sometimes quite flat, or only slightly arched. The wide difference in the principle of construction is obvious. The great object in the Catacombs has been to obtain the maximum of wall-surface, for the interment of the dead in the loculi with which the galleries are lined throughout, with the minimum of excavation. The structural difference will at once be seen by comparing the irregular windings of the small arenarium represented in the upper part of [Figs. 3] and [26] with the straight and symmetrical galleries of the adjacent Catacomb. Connected with the Catacomb of St. Agnes is an extensive arenarium, whose spacious, grotto-like appearance is very different from that of the narrow sepulchral galleries beneath. In the floor of this arenarium is a square shaft leading to the Catacomb, in which Dr. Northcote conjectures there was formerly a windlass for removing the excavated material. There are also footholes, for climbing the sides of the shaft, cut in the solid tufa, perhaps as a means of escape in the time of persecution. This arenarium, which was probably worked out and abandoned long before its connection with the Catacomb, may have been employed as a masked entrance to its crypts, when the more public one could not be safely used. Its spacious vaults may also have been a receptacle for the broken tufa removed from the galleries beneath.
