The Mausoleo Adriano was erected by Adrian, in the gardens of Domitian. It is two stories high; the lower square, the upper round. It was formerly covered with Parian marble, and encircled by a concentric portico, and surmounted by a cupola. The Pons Ælius was the approach to it; during the middle ages, it was used as a fortress; and the upper works, of brick, were added to it by Alexander VI.; when it became the citadel of Rome. This castle was of great service to Pope Clement VII., when the city was surprised (A. D. 1527) by the imperial army. The castle was formerly the burial-place of the Roman emperors, which, after Augustus’s mausoleum on the side of the Tiber was filled with arms, Adrian built for himself and his successors; hence it acquired the name of Moles Hadriani. The large round tower in the centre of the edifice was formerly adorned with a considerable number of small pillars and statues; but most of them were broken to pieces by the Romans themselves, who made use of them to defend themselves against the Goths, when they assaulted the city; as may be read at large in Procopius and Baronius. On the top of it stood the Pigna, since in the Belvidere Gardens. It received its name of St. Angelo, from the supposed appearance of an angel, at the time of a pestilence, during the reign of Gregory the Great. It was fortified by Pope Urban VII., with five regular bastions, ramparts, moats, &c. The hall is adorned with gildings, fine paintings, and Adrian’s statue, whose bust, with that of Augustus, is to be seen on the castle wall.