The Mausoleum of Hadrian, usually known as the Castel Sant'Angelo,
is a towering cylindrical building in Rome. 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.
Much of the tomb contents and decoration has been lost since the
building's conversion into a military fortress in 401 and inclusion
by Flavius Augustus Honorius in the Aurelian Walls.
The Papal state used Sant'Angelo as a prison. Giordano Bruno was
imprisoned there for six years. Executions were carried out by the
Catholic Church in the small interior square. As a prison, it was
also the setting for the third act of Giacomo Puccini's Tosca from
whose ramparts the eponymous heroine of the opera leaps to her death.