Castel Sant’Angelo, Rome.

“The Mausoleum of Hadrian, usually known as Castel Sant’Angelo (English: Castle of the Holy Angel), is a towering cylindrical building in Parco Adriano. 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.”