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 B will be observed the employment of masonry to strengthen the crumbling walls of the friable _tufa_. The descent 33 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[19] 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 Γ Γ Γ, 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, Ω Ω Ω, 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 Catacomb has been excavated in low ground, as in the 34 exceptional case of that of Castulo on the Via Labicana, the water has rendered it completely inaccessible. Access to these different _piani_ is gained by stairways, which are sometimes covered with tile or marble, or built with masonry, or by shafts. The awful silence and almost palpable darkness of these deepest dungeons is absolutely appalling. They are fitly described by the epithet applied by Dante to the realms of eternal gloom: _loco d’ogni luce muto_--a spot mute of all light. Here death reigns supreme. Not even so much as a lizard or a bat has penetrated these obscure recesses. Nought but skulls and skeletons, dust and ashes, are on every side. The air is impure and deadly, and difficult to breathe. “The cursed dew of the dungeon’s damp” distills from the walls, and a sense of oppression, like the patriarch’s “horror of great darkness,” broods over the scene.