In Assassin's Creed Origins, Siwa is Bayek's home and the starting point of his story.
Bayek of Siwa is a Medjay, a protector and law-enforcement figure in Ptolemaic Egypt. The game opens in the Siwa Oasis, where Bayek returns and begins pursuing a masked enemy connected to the wider political and religious conflict of the period.
Siwa is a desert oasis in western Egypt, far from the Nile Valley's largest urban centers. Alexandria, Memphis, and Thebes are all important historical places and appear as locations or references in the game, but none is Bayek's home. His identity is repeatedly tied to Siwa in both dialogue and the game's character presentation.
Origins later follows Bayek and Aya across Egypt as they confront the Order of the Ancients. Their experiences help explain the origins of the Hidden Ones, the organization that later becomes the Assassin Brotherhood. The game's title signals this foundational focus.