The ("Mamertine prison") took the place, as death chamber, of the older quarry caverns that here ran deep into the Capitoline hill. It was apparently built in the 3rd century B.C.
Alban stone—the hardest material available—was used. The chamber was a truncated cone, about i2ft. high. It originally had a ceiling of oak beams, and could be entered only from a trap-door above. In the 2nd century an arc of the circle was cut away to make room for the road in front, and a straight wall of Grotta Oscura stone was built in its place. About ioo B.C. an upper vaulted chamber of Mt. Verde and Anio stone was constructed above the Tullianum, and later the lower chamber was given a horizontal stone vault. Finally, in the reign of Tiberius, a massive facade of travertine was built on the forum front. This is the chamber where noted prisoners like Jugurtha, the Catilinarian con spirators and Vercingetorix were kept before execution. It could never have been a well-house, as has been supposed, since the floor is actually above the republican level of the comitium. The pres ent floor is about 6ft. above the original, if Sallust's measure of its depth is correct.
On the south of the Tullianum are the remains of the Temple of Concordia.' The original temple was erected to the deified ab straction of Concord in 366 to mark the temporary peace in the class conflict between the patricians and plebeians. The temple was rebuilt, partly with the earlier materials, and enlarged by the aristocratic consul Opimius in 120 B.C., to mark the end of the Gracchan class contests. The rededication to Concord was how ever considered an insult by the defeated Gracchans. Here Cicero delivered two of his Catilinarian speeches, using the temple for his addresses not only because he wished to remind the people of his programme of concordia ordinum but also because of the sugges tive proximity of the place to the death-chamber. Tiberius re built the temple in marble to commemorate the Concord of the Augustan regime. This new temple had a large portico and en trance on the forum side and the concrete base of this comes for ward nearly to the Vulcanal. Portions of the elaborately carved cornice and of some of the capitals and bases are still to be seen in the corridor of the Tabularium. The temple was one of the
most richly decorated at Rome and became a veritable museum of precious works of art. The corner of the podium nearest the prison originally belonged to the senaculum—a gathering place of senators—but was incorporated in the enlarged portico of this later temple.
Below the steps of the temple of Concord may be seen the re mains of a very old Altar of Vulcan cut in the native cappellaccio, and near by several cuttings in the rock which give evidence of an early cemetery here. Passing the Arch of Septimius Severus, a work of pleasing proportions though covered with confused re liefs of a decadent and boastful art, we reach the remains of the old Rostra, the scene of Rome's legislative struggles from the time of the Twelve Tables till Caesar. It is the birthplace of modern democracy. In the centre of the mass may be seen a few of the old steps that may belong to the platform of the decemviral times. The name rostra derived from the iron rams taken as trophies from the warships of Antium (338 B.c.) and fastened on the back of the platform (on the forum side). The outer steps of Mt. Verde stone on the side of the Comitium and the circular rear wall of concrete lined with reticulate blocks belong to a rebuilding of the Sullan period.
Between the rostra and the Arch lies a black stone pavement that marks a sacred area uncovered in the excavations of 1899. Roman Buildings of the Republic, 39 ff.
The layer of gravel which covered this area as well as the pre-Sul lan rostra shows that the sacred area was abandoned and covered up when the Sullan rostra were built. The objects found beneath the black stone are a 6th-century inscription of very great impor tance, though so much damaged that no line is complete, a trun cated cone which probably supported a statue, a double base which, according to Varro, supported two figures of lions, pre sumably such as Etruscans placed in front of important tombs, and a great many votive objects of different periods—now to be seen in the forum museum. Some of these objects were found in their original setting, others had been removed here and buried as being too sacred to destroy at the time when the rostra were rebuilt.