Anbar is Basim Ibn Ishaq's hometown before he joins the Hidden Ones in Assassin's Creed Mirage.
Basim begins the game as a street thief in Anbar, a settlement near Baghdad. After a dangerous encounter involving an ancient artifact, he leaves his old life and travels to the Hidden Ones' bureau in Baghdad. There, Roshan trains him as an initiate and eventually accepts him into the organization.
Mirage is set in ninth-century Baghdad during the Islamic Golden Age. The city is the main setting, but Anbar provides the personal starting point for Basim's transformation. This distinction matters because Baghdad is where much of the game takes place, whereas Anbar is the hometown asked for here.
Basim previously appeared in Assassin's Creed Valhalla. Mirage explores his earlier life and his development before the events of that later-set game.