In the original Assassin's Creed, Altaïr's first major mission city is Damascus.
Altaïr Ibn-La'Ahad begins the 1191 campaign in Masyaf, the Assassins' mountain stronghold, but his first major assassination target is in Damascus. The city is one of three principal locations in the game's Holy Land setting, alongside Jerusalem and Acre.
The game uses a fictionalized version of the Third Crusade era. Damascus is presented as a major urban center under Muslim control, with markets, rooftops, guarded districts, and investigation activities that establish the game's stealth-focused structure.
Masyaf is often mistaken for the answer because it is Altaïr's home base and the location of the opening sequence. However, Masyaf is a fortress settlement, while Damascus is the first principal city visited for an assassination contract.