Castel Sant' Angelo

Castel Sant'Angelo was originally the mausoleum of the emperor Hadrian but then it was converted to a fortress for the popes in rge 6th century. In fact, the walls that separate the Vatican CIty from the rest of Rome has a wall that would allow an 'escape' for the pope in case the Vatican was being attacked. This escape route saved one pope's life. The 'fortress' was named Castel Sant'Angelo by Pope Gregory the Great in 590 AD after he saw a vision of an angel above the structure marking the end of the plague in Roma.