Altaïr Ibn-La'Ahad's story in the first Assassin's Creed game is primarily set in 1191.
The game takes place during the Third Crusade, a period of conflict involving European crusaders, Muslim forces, and major cities in the Levant. Altaïr's missions take him to Jerusalem, Acre, and Damascus, while the Assassin stronghold of Masyaf serves as an important base.
The date is significant because the historical setting is not simply medieval Europe. Assassin's Creed combines real events and places with fictional characters and an invented secret war between the Assassins and Templars. Altaïr's targets are often connected to recognizable political and military figures of the Crusades.
Players sometimes confuse the game's setting with the dates of later Assassin's Creed stories. Ezio's adventures occur during the Italian Renaissance, while Assassin's Creed Origins goes much further back to ancient Egypt. The 1191 setting belongs specifically to Altaïr's first major adventure.