On the left of the Appian Road, where it dips suddenly into a valley near the Church of S. Sebastian, lies a group of ruins, the principal of which consist of a circus, a building enclosed in a large square court, and some remains of rooms apparently belonging to an ancient villa. The walls of the circus are still in such preservation that they can be easily traced round the whole enclosure, and are in some parts nearly of the original height. They are built of rubble mixed with brickwork, and with jars of terra-cotta to lighten their weight, as in the case of the masonry in other walls of the same date. The towers at each side of the Carceres, or starting post, the curved line of Carceres themselves, and the spina, or central division line, can be easily traced. An inscription in honour of Romulus, son of Maxentius, found here in 1825, and now placed at the entrance to the ruins, seems to show the circus was built in honour of Romulus, son of Maxentius, who died before his father, A.D. 309. This is confirmed by a statement in one of the ancient chronicles published by Roncalli, in which it is said that Maxentius built a circus near the catacombs, evidently referring to the neighbouring catacombs of S. Sebastian and others, and also by the style of masonry used in the circus. The adjoining ruined temple, with its enclosing court, seems to belong to a somewhat earlier style of construction, but some reasons derived from the coins of Maxentius and Romulus have been given for supposing that it was the temple dedicated to Romulus after his apotheosis by his father.[131] The ruins are not sufficiently preserved to make it certain that the building was a temple, and there is nothing to contradict the hypothesis that it was a tomb. Nor is anything whatever known about the adjoining villa. [Sidenote: Tomb of Cæcilia Metella.] On the end of the mound formed by the great lava stream which ages ago flowed down from the Alban Hills, and along the top of which the Via Appia runs from this point, stands the conspicuous Tomb of Cæcilia Metella, the daughter of Metellus Creticus, and wife of Crassus, but whether of the Triumvir Crassus, or of the orator, or of some other less well known Crassus is uncertain. The inscription on the tomb is Cæciliæ, Q. Cretici Filiæ, Metellæ Crassi. The shape of the tomb is the same as that of the Mausoleum of Hadrian, and the Tomb of the Plautii at Tivoli; a cylindrical towerlike edifice, resting on a square base of concrete with massive blocks of travertine. The upper part has been destroyed, and the marble casing stripped off, with the exception of a band of ox skulls and garlands which surrounds it, and some trophies carved in relief above the inscription. The roof was probably conical. Mediæval battlements, erected by the Caetani family, who held it as a fortress in the 13th century, now crown the upper edge. The remains of their castle are still visible on each side of the road beyond the tomb.