Located in Parco Adriano, the Mausoleum of Hadrian is perhaps better known to the public as Castel Sant'Angelo. The structure was commissioned by Emperor Hadrian as a resting place for himself and his family. It was built between AD 134 and 139. Hadrian's ashes were laid placed inside in 138 and the tradition to lay other emperors to rest here was born. Later it was used by the popes as a fortress. Nowadays, the Mausoleum of Hadrian is a museum.