Which historical era is depicted in the main story of the first Assassin's Creed?

The main story of the first Assassin's Creed is set during the Third Crusade.

The historical sections take place in the Levant in 1191, when Christian and Muslim forces were contesting territory during the Third Crusade. Altaïr Ibn-La'Ahad, an Assassin, carries out missions in Jerusalem, Acre, and Damascus while investigating a network of powerful targets.

The game uses real historical figures, including Robert de Sablé and William of Montferrat, but it places them inside a fictional conflict involving the Assassins, Templars, and Pieces of Eden. This mixture of documented history and invented mythology became a defining feature of the series.

The era is sometimes confused with later Assassin's Creed settings. The Italian Renaissance belongs chiefly to Assassin's Creed II, while the French Revolution is the setting of Assassin's Creed Unity.