The Castel Sant’Angelo, also known as the Mausoleum of Hadrian, is a fascinating site. It started as a Roman tomb, was converted into a fortress, and was used as a papal refuge and a prison. An above-ground fortified passageway connects the fortress with the Vatican.
I took these photos on the same day (May 7, 2015), standing on the bridge that leads from the main part of the historic area of Rome to the Vatican.