Castel Sant Angelo 1 - The Mausoleum Of Hadrian, Usually Known As The Castel Sant'Angelo (English: Castle Of The Holy Angel), 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 Popes Converted The Structure Into A Castle, Beginning In The 14th Century; Pope Nicholas III Connected The Castle To St. Peter's Basilica By A Covered Fortified Corridor Called The Passetto Di Borgo. The Fortress Was The Refuge Of Pope Clement VII From The Siege Of Charles V's Landsknechte During The Sack Of Rome (1527), In Which Benvenuto Cellini Describes Strolling The Ramparts And Shooting Enemy Soldiers. Photo