In 1277, a half-mile-long elevated covered passageway, the Passetto di Borgo, was constructed to link the Vatican with the fortified Castel Sant'Angelo on the banks of the Tiber River. It served as an escape route for popes, most notably in 1527 when it likely saved the life of Pope Clement VII during the sack of Rome.
As the forces of Holy Roman Emperor Charles V rampaged through the city and murdered priests and nuns, the Swiss Guard held back the enemy long enough to allow Clement to safely reach the Castel Sant'Angelo, although 147 of the pope's forces lost their lives in the battle.