The mausoleum was started around the year 130 A.D. and completed in 139, one year after the death of Emperor Hadrian (117-138 A.D.). It stood on the right bank of the Tiber and could be accessed from Campus Martius through Ponte Elio (Pons Aelius), today Ponte Sant’Angelo.
It consists of a square pedestal and a circular construction (drum) which today forms the lower part of Castel Sant’Angelo. The gallery that runs around the drum, reaches a corridor that leads to the burial chamber, located at the center of the mausoleum. The chamber is a square room with three niches on the sides, once covered with marble.
The urn with Hadrian’s ashes was placed here and later all the emperors of the Antonini and Severi families up to Caracalla were buried here. A bronze quadriga with the statue of Hadrian was placed on top of the mausoleum.
The building was later included within a rampart of the Aurelian Walls, perhaps by Emperor Honorius in 403 A.D.. It was transformed into a castle probably in the tenth century.