The Passetto

The Passetto is the corridor old Vatican wall between St. Peter's and the Castel Sant' Angelo. This 800m long passageway is also known as the Passetto di Borgo. It was located in the rione of Borgo. It was erected in 1277 by Pope Nicholas III, but parts of the wall were built by Totila during the Gothic War. From outside it looks like a wall but inside there is the tunnel, which on several occasions served as an escape route for Popes in danger. Pope Alexander VI crossed it in 1494, when Charles VIII invaded the city and the Pontiff's life was in danger.

Clement VII escaped to safety through this passage during the Sack of Rome in 1527. Troops of the Holy Roman Emperor, Charles V, massacred almost the entire Swiss Guard on the steps of St Peter's Basilica as the guard protected the Pope, buying him time to escape through the Passetto.
It played a key role in the Dan Brown novel Angels & Demons, through which the antagonist transported four abducted cardinals to the Castle of Sant' Angelo. The protagonists Robert Langdon and Vittoria Vetra later used the Passetto as a shortcut to Vatican City.