This building has had a checkered history. Originally a dynastic tomb, it was converted into a fortress, then became a noble dwelling and finally a papal residence; between times it served as a barracks, a prison and a museum.
Hadrian (117-38 AD) built a tomb in Domizia's gardens that was to become the dynastic sepulcher of the Antonines. Work started in 123 but was only completed in 139, after's death. The Pons Aelius (the predecessor of the Ponte Sant'Angelo 239), inaugurated in 134, linked the monument to the Campo Marzio.
The Sepulchral Chamber. The present entrance (which is about 10 feet above the level of the ancient one) leads via a short corridor to a square hall. The semicircular niche hollowed out in the back wall was probably intended to contain a statue of Hadrian. On the right is a spiral ramp leading to the cella (mortuary chamber), the heart of the monument. In this square room, which was originally faced with marble, the funerary urns of Emperor Hadrian and his wife, sabina.
Sant'Angelo was Rome's most important fortified area, anyone who held it had virtually the whole town at his mercy. Consequently, its history reflected the city's turbulent internal conflicts. Between the 10th and 11th centuries it passed into the hands of the most powerful noble families before suffering a massive attack by the Roman people, who made up their minds to demolish it in 1379.
Fortifications and Modifications. Under Nicholas III the castle became papal property. Most of the alterations to the building carried out between the pontificates of Nicholas V (1447-55) and Urban VII (1623-44) had a military purpose. Access to the subterranean galleries was blocked, two towers were built at the entrance and four bastions at the corners, a moat was dug, pentagonal ramparts were erected with five small forts (today no longer standing) and, finally the Corridoio or Passetto, the fortified passageway linking St Peter's to the castle, was strengthened.