Siwa is Bayek's home in Assassin's Creed Origins.
Bayek is a Medjay, a protector and lawkeeper, from the Siwa Oasis in the Western Desert of Egypt. The game opens in this region and uses Bayek's return there to establish his personal motivations and his relationship with Aya.
Alexandria, Memphis, and Giza are also important locations in Origins, but none is Bayek's home. Siwa's remote oasis setting helps explain Bayek's distinct identity and his role between local Egyptian traditions and the changing political world shaped by Rome and the Ptolemaic kingdom. Origins is set before the formal Assassin Brotherhood seen in later historical periods.