Castel S.Angelo and Tiber. Also in autumn Rome is a Sunny city. Castel S.Angelo was initially a mausoleum for the Roman Emperor Hadrian and his family. It was later used by the popes as a fortress and castle and it is connected 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).