Later, this building was used as a Papal prison for people like Benvenuto Cellini, who famously escaped.
After leading a rebellion against Gregory V, Crescentius the Younger hid in this place before he was captured and executed. According to legend, Decio Azzolino's lateness to a meeting with Christina of Sweden led her to fire a cannonball at the Villa Medici from the roof of this building. Yves d'AllÃ¨gre's meeting with a woman at this location in 1501 led to her renouncement of ForlÃ¬ and Imola. Earlier, that wife of Girolamo Riario held this building while seven months pregnant, attempting to control the succession of Sixtus IV. This place was held by Caterina Sforza, and was renamed when the end of a plague in 590 was signaled by the (*) appearance of the Archangel Michael. Vibia Sabina, Julia Domna, and Caracalla are buried in this structure, which was built as a mausoleum for Hadrian. Later, this building was used as a Papal prison for people like Benvenuto Cellini, who famously escaped. For 10 points, name this cylindrical fortress in Rome located just outside the Vatican.
After leading a rebellion against Gregory V, Crescentius the Younger hid in this place before he was captured and executed.
 Castel Sant' Angelo 