In Assassin's Creed Brotherhood, what is the name of the papal fortress Ezio infiltrates in Rome?

In Assassin's Creed Brotherhood, Ezio infiltrates Castel Sant'Angelo in Rome.

Castel Sant'Angelo is a historic fortress beside the Tiber River. In Brotherhood's story, it is associated with the Borgia pope Rodrigo Borgia and his son Cesare Borgia. Ezio's assault on the fortress forms part of the campaign against the Borgia regime that controls Rome.

The building began as the Mausoleum of Hadrian in the second century CE and was later converted into a military fortress. Its papal connections and defensive position made it an appropriate setting for the game's climactic missions. The game recreates a fictionalized Renaissance version of Rome while incorporating the real monument's recognizable architecture.

Castel Sant'Angelo should not be confused with the Auditore family's Villa Auditore in Monteriggioni, or with Florence's Palazzo della Signoria. Those locations are important elsewhere in the series but are not the papal fortress Ezio infiltrates in Brotherhood.