Masyaf is the fortress that serves as the Assassins' headquarters in Assassin's Creed Revelations.
The game begins with Ezio Auditore traveling to Masyaf, a mountain stronghold associated with the Levantine Brotherhood and Altaïr Ibn-La'Ahad. Ezio seeks information connected to Altaïr and the keys to the ancient fortress library. The location links the stories of Ezio and Altaïr across different historical periods.
Masyaf was already established in the first Assassin's Creed game, where it serves as Altaïr's home base. In Revelations, it appears as a significant narrative location, while most of the game's open-world exploration takes place in Constantinople, now Istanbul, during the early sixteenth century.
Alamut is a real fortress often associated in popular history with the Nizari Ismailis, but it is not the headquarters asked for here. Monteriggioni is Ezio's Italian base in earlier games. These similar fortress names make Masyaf an especially useful distinction within the series' fictionalized history.