A modern staircase leads to the horrible dungeon of Ancus Martius, sixteen feet in height, thirty in length, and twenty-two in breadth. Originally there was no staircase, and the prisoners were let down there, and thence into the lower dungeon, through a hole in the middle of the ceiling. The large door at the side is a modern innovation, having been opened to admit the vast mass of pilgrims during the festa. The whole prison is constructed of huge blocks of tufa without cement. Some remains are shown of the _Scalæ Gemoniæ_, so called from the groans of the prisoners--by which the bodies were dragged forth to be exposed to the insults of the populace or to be thrown into the Tiber. It was by this staircase that Cicero came forth and announced the execution of the Catiline conspirators to the people in the Forum, by the single word _Vixerunt_, "they have ceased to live." Close to the exit of these stairs the Emperor Vitellius was murdered. On the wall by which you descend to the lower dungeon is a mark, kissed by the faithful, as the spot against which St. Peter's head rested. The lower prison, called _Robur_, is constructed of huge blocks of tufa, fastened together by cramps of iron and approaching horizontally to a common centre in the roof. It has been attributed from early times to Servius Tullius; but Ampère[47] argues against the idea that the lower prison was of later origin than the upper, and suggests that it is Pelasgic, and older than any other building in Rome. It is described by Livy, and by Sallust, who depicts its horrors in his account of the execution of the Catiline conspirators.[48] The spot is shown to which these victims were attached and strangled in turn. In this dungeon, at an earlier period, Appius Claudius and Oppius the decemvirs committed suicide (B.C. 449). Here Jugurtha, king of Mauritania, was starved to death by Marius. Here Julius Cæsar, during his triumph for the conquest of Gaul, caused his gallant enemy Vercingetorix to be put to death. Here Sejanus, the friend and minister of Tiberius, disgraced too late, was executed for the murder of Drusus, son of the emperor, and for an intrigue with his daughter-in-law, Livilla. Here, also, Simon Bar-Gioras, the last defender of Jerusalem, suffered during the triumph of Titus.