In Assassin's Creed Origins, Bayek's home at the start of the story is Siwa.
Siwa is an oasis in Egypt's Western Desert and the home of Bayek, a Medjay, and his wife Aya. The opening chapters establish Bayek's personal motivations and introduce the masked figures whose actions drive his pursuit across Ptolemaic Egypt.
The game later expands into a large open world that includes Alexandria, Memphis, Giza, the Nile Valley, and desert regions. Siwa therefore represents the beginning of Bayek's journey rather than the whole of the Egyptian setting. Its remote location also helps explain Bayek's role as a local protector and guide.
Origins is set in the first century BCE, during the reign of Cleopatra VII and the political struggle involving Julius Caesar and Ptolemy XIII. The game presents the formation of the Hidden Ones, the organization that later develops into the Assassin Brotherhood.