Castel Sant'Angelo is one of Rome's favorite and most-recognized monuments. Yet many do not know that this impressive castle was also the Mausoleum of Hadrian, thus making it one of the city's largest funerary monuments.
Connected to Campo Marzio (military neighborhood used for important funerals of State) by way of a bridge, the Mausoleum hosted the remains of the Emperor Hadrian, along with those of his successors, down to Caracalla.
Source: http://www.italia.it