Let us now descend from the Capitoline Piazza towards the Forum, by the staircase on the left of the Palace of the Senator. Close to the foot of this staircase is a church, very obscure-looking, with some rude frescoes on the exterior. Yet every one must enter this building, for here are the famous _Mamertine Prisons_, excavated from the solid rock under the Capitol. The prisons are entered through the low Church of S. Pietro in Carcere, hung round with votive offerings and blazing with lamps. "There is an upper chamber in the Mamertine Prisons, over what is said to have been--and very possibly may have been--the dungeon of St. Peter. The chamber is now fitted up as an oratory, dedicated to that saint; and it lives, as a distinct and separate place, in my recollection, too. It is very small and low-roofed; and the dread and gloom of the ponderous, obdurate old prison are on it, as if they had come up in a dark mist through the floor. Hanging on the walls, among the clustered votive offerings, are objects, at once strangely in keeping and strangely at variance with the place--rusty daggers, knives, pistols, clubs, divers instruments of violence and murder, brought here, fresh from use, and hung up to propitiate offended Heaven; as if the blood upon them would drain off in consecrated air, and have no voice to cry with. It is all so silent and so close, and tomblike; and the dungeons below are so black, and stealthy, and stagnant, and naked; that this little dark spot becomes a dream within a dream: and in the vision of great churches which come rolling past me like a sea, it is a small wave by itself, that melts into no other wave, and does not flow on with the rest."--_Dickens._ Enclosed in the church, near the entrance, may be observed the outer frieze of the prison wall, with the inscription C. TIBIUS. C. F. RUFINUS. M.. COCCEIUS. NERVA. COS. EX. S. C., recording the names of two consuls of A.D. 22, who are supposed to have repaired the prison. Juvenal's description of the time when one prison was sufficient for all the criminals in Rome naturally refers to this building: "Felices proavorum atavos, felicia dicas Sæcula, quæ quondam sub regibus atque tribunis Viderunt uno contentam carcere Romam." _Sat._ iii. 312.