(The Catacombs (except those at S. Sebastiano) can only be visited in company of a guide. For most of the Catacombs it is necessary to obtain a _permesso_ at the office of the Cardinal-Vicar, 70 Via della Scrofa, before 12 A.M.; upon which a day (generally Sunday) is fixed, which must be adhered to. The Catacombs of St. Calixtus are sometimes superficially shown without a special _permesso_. It may be well for the visitor to provide himself with tapers--_cerini._) All descriptions of dangers attending a visit to the Catacombs, if accompanied by a guide, and provided with "cerini," are quite imaginary. Neither does the visitor ever suffer from cold; the temperature of the Catacombs is mild and warm; the vaults are almost always dry, and the air pure. "The Roman Catacombs--a name consecrated by long usage, but having no etymological meaning, and not a very determinate geographical one--are a vast labyrinth of galleries excavated in the bowels of the earth in the hills around the Eternal City; not in the hills on which the city itself was built, but in those beyond the walls. Their extent is enormous; not as to the amount of superficial soil which they underlie, for they rarely, if ever, pass beyond the third mile-stone from the city, but in the actual length of their galleries; for these are often excavated on various levels, or _piani_, three, four, or even five--one above the other; and they cross and recross one another, sometimes at short intervals, on each of these levels; so that, on the whole, there are certainly not less than 350 miles of them; that is to say, if stretched out in one continuous line, they would extend the whole length of Italy itself. The galleries are from two to four feet in width, and vary in height according to the nature of the rock in which they are dug. The walls on both sides are pierced with horizontal niches, like shelves in a bookcase or berths in a steamer, and every niche once contained one or more dead bodies. At various intervals this succession of shelves is interrupted for a moment, that room may be made for a doorway opening into a small chamber; and the walls of these chambers are generally pierced with graves in the same way as the galleries.