The Castel St. Angelo is approached by the Ponte S. Angelo, (Bridge of Angels), which is one of eight bridges over the Tiber River.
The Ponte S. Angelo is know as the "gateway" to St. Peters and the Vatican and dates from Roman times.

The bridge is decorated on both sides with sculpted angels, each bearing one of the instruments of Christ's passion.
The angels were designed by Gianlorenzo Bernini, who was in charge of the interior decoration of St. Peters,
as well as the builder of the immense colonnade surrounding Pza. S. Peters.
All but two of the angels (seen in the next two images) were sculpted by Bernini's assistants.
The Angel with the Crown of Thorns and the Angel with the Superscription INRI, are mostly by Bernini's hand,
though the ones on the bridge are actually copies. (See next two images)

In the background is the Castel St. Angelo, which was originally built (130-139 AD) as Hadrian's Mausoleum .
It became a prison and then a safe haven for Popes in times of threat or invasion.
A covered corridor known as the Passeto di Borgo, connects the Castel with the Vatican.
Pope Clement VII sought refuge there from the troops of Charles de Bourbon's army during the Sack of Rome in 1527,
fleeing the Vatican through that secret passagetto.

The Castel S. Angelo, originally containing beautifully decorated Papal Apartments, as well as prisons and a torture chamber,
is now a museum