In the year 590, as he prayed for Rome's deliverance from a plague, St. Gregory the Great had an encouraging vision of an angel sheathing its sword above this massive brick castle built atop the drum of Hadrian's first-century mausoleum. The plague ended, and the castle got a new name (and, in 1752, a spiffy bronze statue of the angel). Subsequent popes added rooms, creating a veritable (and highly decorative) labyrinth, which also has a scandalous past. Castel Sant'Angelo is connected to the Vatican by the passetto, a long wall topped by covered passage allowing the pope to scurry to his stronghold in time of need—as did Pope Clement VII did during the sack of Rome in 1527. It was the only known time a Pope used the Swiss Guard as a human shield, leaving the bulk of them to die covering his escape. Castel Sant'Angelo has some of the most spectacular views of Rome from its rooftop terrace.