The Passetto (small passage) is the corridor atop the old Vatican wall between St. Peter's and the Castel Sant' Angelo. This 800m long passageway is also known as the Passetto di Borgo (the district where it's located), or in earlier times, the Corridore di Borgo. During the Sack of Rome in 1527, it was used by Pope Clement VII to escape to the Castel Sant' Angelo