30 Minutes 
The mausoleum was probably begun around 130 AD and finished in 139, a year after the death of the emperor Hadrian (117-138 AD).
It stood on the right bank of the Tiber and was accessible from Campo Marzio by means of Ponte Elio, the current Ponte Sant'Angelo.
It consists of a square base and a circular construction (drum) which currently constitutes the lower part of Castel Sant'Angelo.
Through a gallery that goes around the tambour, you enter a corridor that leads to the burial chamber, located in the center of the mausoleum. The environment is a square room, with three niches on the sides, formerly covered with marble. Here was the urn with Hadrian's ashes and subsequently all the emperors of the Antonini and Severi families were deposed there up to Caracalla.
On the top of the mausoleum there was a bronze quadriga with the statue of Hadrian. Later the building was included in a bastion of the Aurelian walls, perhaps by the emperor Honorius in 403 AD.
It was probably transformed into a castle in the 10th century.
