The main story of the original Assassin's Creed takes place in 1191.
The game follows Altaïr Ibn-La'Ahad during the Third Crusade, when he operates in cities including Masyaf, Jerusalem, Acre, and Damascus. The date places the historical sections during the conflict between Crusader and Muslim forces in the medieval Levant.
The game's science-fiction framing adds modern scenes involving Desmond Miles and the Animus, but the principal historical adventure occurs in 1191. This distinction matters because the narrative moves between a contemporary storyline and memories reconstructed from Altaïr's ancestor.
The original game is sometimes confused with the date of the First Crusade or with later Assassin's Creed settings. It is not set in 1099, the year Jerusalem was captured during the First Crusade. Its 1191 setting instead aligns with the Third Crusade and the reign of figures such as Richard the Lionheart and Saladin.