Castel Sant'Angelo is an imposing fortress on the banks of the Tiber. It was originally Hadrian's mausoleum, but was converted into a Papal fortress in the 6th Century and used through the sack of Rome in 1527. There is a secret passageway that leads to the Vatican Palaces.
Ponte Sant'Angelo with the Basilica of St. Peter's in the distance.
Ponte Sant'Angelo is a footbridge across the Tiber in front of the fortress. The original arches of the bridge were built by Hadrian in 136 CE, and later expanded upon as the banks of the Tiber were widened. Bernini added splendid pairs of angels across the bridge in the 17th Century.