This building was initially commissioned by the Roman Emperor Hadrian as a mausoleum for himself and his family. The building was later used by the popes as a fortress and castle, and is now a museum.
It was built between 135 AD and 139 AD. Originally the mausoleum was a decorated cylinder, with a garden top and golden quadriga. Hadrian's ashes were placed here a year after his death in Baiae in 138 AD, together with those of his wife Sabina, and his first adopted son, Lucius Aelius, who also died in 138 AD. Following this, the remains of succeeding emperors were also placed here, the last recorded deposition being Caracalla in 217 AD. The urns containing these ashes were probably placed in what is now known as the Treasury room deep within the building.1