*

in Fig. 9. The walls and ceiling were often covered with fresco paintings, frequently of elegant design, to be hereafter described. Sometimes, as in some examples in the Catacomb of St. Agnes, tufa or marble seats are ranged around the chamber, and chairs are hewn out of the solid rock. These chambers were used probably for the instruction of catechumens. Occasionally the cubiculum terminates in a semicircular recess, as in the upper chamber in Fig. 9. These probably gave rise to the apse in early Christian architecture, of which a good example is found in the Church of St. Clement, one of the most ancient Christian edifices in Rome. Niches and shelves for lamps, an absolute necessity in the per petual darkness that there reigns, frequently occur, such as may be seen in Italian houses to-day. Without the least authority, some Roman Catholic writers have de..

* Book II.

See Fig. 130 and context, where the entire subject is discussed.

scribed these as closets for priestly vestments and shelves for pictures.

A peculiar form of grave common in these chambers, as well as in the galleries, is that known as the arcosolium, or arched tomb. It consists of a recess in the wall, having a grave, often double or triple, excavated in the tufa, or built with masonry, like a solid sarcophagus, and closed with a marble slab. These are seen in the plan, Fig. 9, in the section, Fig. 10, at G and E in Fig. 15, and in perspective in Figs. 11 and 12. Sometimes the recess is rectangular instead of arched, and is then called by De Rossi sepolcro a mensa, or table tomb. Sometimes the arch was segmental, especially when constructed of masonry.* An example of both sorts is

Fig. 13.-Cubiculum with Arcosolia.

scen in the accompanying engraving of a cubiculum in the Catacomb of St. Prætextatus. The narrow door into the corridor is also seen, and the stucco capitals and bases of the columns. In course of time these arcosolia were * See in the Cemetery of St. Helena, Fig. 29.

used as altars for the celebration of the eucharist, and eventually grave abuses arose from the superstitious veneration paid to the relics of the martyr or confessor interred therein. Frequently, also, the back of this arched recess was pierced with graves of a later date, often directly through a painting,* in order to obtain a resting place near the bodies of the saints.

Hitherto only one level of the Catacombs has been described, but frequently "beneath this depth there is a lower deep," or even three or four tiers of galleries, excavated as the upper ones became filled with graves. Thus there are sometimes as many as five stories, or piani, as they are called, one beneath the other. These are carefully maintained horizontal, to avoid breaking through the floor of the one above or the roof of the one below, the danger of which would be very great if the strict level were departed from. For the same reason the different piani were generally separated by a thick stratum of solid tufa. The relative position of these levels is shown by the following engraving, reduced from De Rossi. It represents a section of the Crypt of St. Lucina, a part of the Cemetery of Callixtus. The dark colored stratum, marked 1 in the margin, is entirely made up of the debris of ancient monuments, buildings, and other materials accumulated in the course of ages in this place to the depth of eight feet. It has completely buried the ancient roads, except where excavated, as shown in the engraving. The next stratum, II, is of solid grayish tufa. In this the first level or piano, , is excavated. It is not more than twenty feet below the surface, and in many places only half that depth. Consequently its area is comparatively limited, because if extended it would have run out into the

*As in Fig. 12, and more strikingly in Fig 76.

open air, from the sloping of the ground in which it is dug. The next stratum, III, is softer and more easily worked, and therefore is that in which are found the most important and extensive piani of galleries. The cross sections P and X, and the longitudinal section u, will show how the lower surface of the more solid stratum above was made the ceiling of these galleries, in order to lessen the danger of its falling. At в will be observed the employment of masonry to strengthen the

crumbling walls of the friable tufa. The descent of a few steps, some of which have been worn away, will also be noticed at u. At iv a more rocky stratum is found, called tufa lithoide, below which the ancient fossors* had to go to find suitable material for the excavation of the third piano. This was found in stratum v, in which are two piani at different levels. The lower one is not vertically beneath that here represented above it, but at some little distance. It is here shown, to exhibit at one view a section of all the stories of this Catacomb. The upper piano, g, consists of low and narrow galleries, but the lower one, marked гr г, seventy-one feet beneath the surface of the ground, is of great extent. Several of the loculi, it will be perceived, are built of masonry, in consequence of the crumbling nature of the soil. The three large arcosolia will also be observed. The floor of this piano rests on a somewhat firmer stratum, in which is still another level of galleries, , ten feet lower down. This lower level is generally subject to inundation by water, in consequence of the periodical rising of the adjacent Almone, the level of which is shown at a depth of one hundred and four feet, and that of the Tiber at one hundred and thirty-one feet, below the surface.

To secure immunity from dampness, which would accelerate decomposition and corrupt the atmosphere, the Catacombs were generally excavated in high ground in the undulating hills around the city, never crossing the intervening depressions or valleys. There is, therefore, no connection between the different cemeteries except where they happen to be contiguous, nor, as has been asserted, with the churches of Rome. Where a

* An organized body of diggers, by whom the Catacombs were ex. cavated. See Book III, chap. iv.