In Assassin's Creed, Altaïr Ibn-La'Ahad is based in Masyaf during the game's opening.
Masyaf is the mountain fortress that serves as the headquarters of the Assassin Brotherhood in the original game. Altaïr returns there after missions and receives instructions from Al Mualim, the Brotherhood's leader. The settlement is presented as both a military stronghold and a hidden home for the Assassins.
The game then sends Altaïr to several major cities in the Holy Land, including Jerusalem, Damascus, and Acre. Those cities are mission locations, which can cause confusion with Masyaf. Masyaf is not one of the principal urban investigation targets; it is the Brotherhood's base and the setting for important story scenes.
The fortress is inspired by the real medieval castle of Masyaf in present-day Syria. Assassin's Creed uses historical locations and figures as the setting for its fictional conflict between Assassins and Templars, while changing details for the game's narrative.