HADRIAN, TOMB or MAUSOLEUM OF (Lat. Hadrianum). The massive building in Rome now known as the Castel Sant' Angelo. It was erected in A.D. 136 by the Emperor Hadrian, to gether with the Mimi Bridge (Ponte Sant' An gelo), which gave access to it. The tomb was situated in the gardens of Domitia, on the bank of the Tiber. It consisted of a basement 247 feet square, surmounted by a circular mass of masonry 230 feet in diameter, both faced with Parian marble. The whole was crowned with a cone of earth planted with evergreens. The tomb was adorned with statues and surrounded by a gilt bronze railing with gilt peacocks, two of which are preserved in the Vatican gardens. The front of the basement had panels bearing the names of the members of the Imperial family buried in the tomb. The entrance to the burial chamber was in the front, facing the bridge. The structure was fortified in the time of Honorius, and was the centre of the factional strife dur ing the mediaeval and modern history of Rome.
The castle was held by the popes from the time of Boniface IX., and about 1500 was connected with the Vatican by a subterranean passage. The ancient structure is almost concealed by the works of fortification which have been added to it, and has been despoiled at various times. The marble tombstones were used by Gregory XIII. in the construction of his Gregorian Chapel in the Vatican, and the mausoleum supplied the materials with which the Sistine Chapel was built. The gilt angel sheathing his sword, and with outstretched wings, on the pinnacle of the struc ture, is a modern work, taking the place of previ ous statues destroyed or stolen during the Mid dle Ages. It commemorates the appearance of the Archangel Michael to Gregory the Great dur ing a plague.