Passing along the bank of the Tiber by the Via Ripetta from the Porta del Popolo we come to the bridge of S. Angelo (Pons Ælius) which crosses the river close to the Castle of S. Angelo, anciently the Mausoleum of Hadrian. This bridge was built by the Emperor Hadrian at the same time with his Mausoleum. The anonymous writer of the Einsiedlen MS. gives an inscription which in his time remained upon the bridge assigning its erection to the nineteenth tribuneship and third consulship of Hadrian, which indicates the year A.D. 135, and in confirmation of this Nardini gives a medal of Hadrian which dates from his third consulship, and has on the obverse a representation of this bridge. The name Pons Ælius, given to it by Dion Cassius in his account of Hadrian’s funeral, was probably derived either from Hadrian’s prænomen Ælius, or from the name of his son Ælius Cæsar whose burial was the first which took place in the Mausoleum. The piers of the bridge are ancient, but the upper parts have been rebuilt. [Sidenote: Mausoleum of Hadrian.] The Mausoleum of Hadrian owes its preservation entirely to the peculiar fitness of the site and shape for the purpose of a fortress which it has served since the time of Belisarius. Had it not been thus made serviceable to the turbulent spirit of the mediæval Romans, the same hands which stripped the great pile of its marble facing, and, after hurling the statues with which it was adorned into the moat, allowed them to lie there in oblivion, would have torn asunder and carried away the whole mass to furnish materials for the palaces and stables of their ferocious and ignorant nobles. The original form of this colossal mausoleum is now greatly changed by the modern buildings which have been piled upon it, by the addition of the corbels round its upper part, and by the loss of the exterior facing of marble, so that the ancient appearance can be only conjecturally restored. The remaining ancient part consists of a square basement of concrete and travertine blocks, the sides of which measured ninety-five yards surmounted by an enormous cylindrical structure of travertine seventy yards in diameter and seventy-five feet high. Procopius tells us that this was cased in Parian marble, and that upon the summit stood a number of splendid marble statues of men and horses.[104] There are several other tombs in Italy constructed upon the same plan with a cylindrical tower placed upon a square base. Two of these are upon the Appian road about three miles from Rome, the celebrated Tomb of Cæcilia Metella, and that of the Servilii, and belong to the Republican Era. Two others are of the Augustan Age, the tomb of the Plautii at Ponte Lucano, near Tivoli, and the beautiful monument of Munatius Plancus, near Gaeta. Hadrian’s design was not therefore by any means a new one, as we might have expected in the case of an emperor who was himself an architect, and proud of his artistic designs.