"He was buried near the river itself, close to the Aelian bridge; for it was there that he had prepared his tomb, since the tomb of Augustus was full, and from this time no body was deposited in it."
Cassius Dio, Roman History (LXIX.23.1)
Until the time of Nerva, the ashes of the Roman emperors had been placed in the Mausoleum of Augustus, although Trajan's remains were put in the base of his column in the Forum of Trajan. Hadrian built a new mausoleum (Mausoleum Hadriani), which was completed by his adoptive son and successor Antoninus Pius in AD 139, the year after Hadrian's death. (The largest tomb in the Roman world was that of Augustus, which Hadrian consciously did not attempt to surpass.) In it were placed the cinerary urns of Hadrian; Antoninus Pius and his wife, Faustina; Lucius Verus; Marcus Aurelius and his son, Commodus; Septimius Severus and his family, Julia Domna, Geta, and Caracalla. And there they remained until the sack of Rome by Alaric and the Visigoths in AD 410. When Aurelian began to surround the city with a new wall (Muri Aureliani) in AD 271, the mausoleum was incorporated as part of the defense and turned into a fortress. (The Pons Aelius that approaches the tomb was built by Hadrian in AD 134, three of its central arches still standing.)
