The main historical story of the original Assassin's Creed is set in 1191. Altaïr Ibn-La'Ahad's missions occur during the Third Crusade, a period of conflict among Crusader and Muslim powers in the eastern Mediterranean.
The game takes Altaïr to the major cities of Masyaf, Jerusalem, Acre, and Damascus. Its plot uses real historical figures and events as a framework for the fictional struggle between the Assassins and Templars. The story's secret organizations, artifacts, and memory technology are fictional additions to that historical setting.
The year 1191 places the game after the 1187 Battle of Hattin and the fall of Jerusalem to Saladin, while the Third Crusade is still underway. Players sometimes associate the game with 1099, the year of the First Crusade's capture of Jerusalem, or with 1187 because of Hattin, but neither is the principal year of Altaïr's campaign.