The Mausoleum of Hadrian, usually known as Castel Sant’Angelo, is a towering cylindrical building in Parco Adriano, Rome, Italy. It 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. The Castel was once the tallest building in Rome.

The tomb of the Roman emperor Hadrian, also called Hadrian’s mole, was erected on the right bank of the Tiber, between 134 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, together with those of his wife Sabina, and his first adopted son, Lucius Aelius, who also died in 138.  Following this, the remains of succeeding emperors were also placed here, the last recorded deposition being Caracalla in 217. The urns containing these ashes were probably placed in what is now known as the Treasury room deep within the building. Hadrian also built the Pons Aelius facing straight onto the mausoleum – it still provides a scenic approach from the center of Rome and the right bank of the Tiber, and is renowned for the Baroque additions of statues of angels holding aloft elements of the Passion of Christ.

Much of the tomb contents and decorations have been lost since the building’s conversion to a military fortress in 401 and its subsequent inclusion in the Aurelian Walls by Flavius Augustus Honorius. The urns and ashes were scattered by Visigoth looters during Alaric’s sacking of Rome in 410, and the original decorative bronze and stone statuary were thrown down upon the attacking Goths when they besieged Rome in 537, as recounted by Procopius. An unusual survivor, however, is the capstone of a funerary urn (probably that of Hadrian), which made its way to Saint Peter’s Basilica, covered the tomb of Otto II and later was incorporated into a massive Renaissance baptistery.