Introduction to Castel Sant'Angelo: Castel Sant'Angelo is located on the banks of the Tiber River, the westernmost point of the ancient Roman region. It is named after the statue of Archangel Michael on the top of the castle. The castle was built in 139 AD as the tomb of Emperor Hadrian. It is now a 58-room museum and is well worth a visit. (ticket 10.5 euros)