Alexandria serves as the main urban hub in Assassin's Creed Origins.
The game is set in Ptolemaic Egypt during the first century BCE, near the end of the Ptolemaic Kingdom. Alexandria is a major center of Greek and Egyptian culture, scholarship, politics, and trade, and the game uses it as one of its most important locations for quests, exploration, and story developments.
The protagonist, Bayek of Siwa, is a Medjay who becomes involved in the origins of the Hidden Ones, the group that later develops into the Assassin Brotherhood. His wife, Aya, is also central to the narrative. The story takes place during the reign of Cleopatra VII and the Roman intervention in Egypt.
Siwa is crucial because it is Bayek's homeland, while Memphis and Cyrene are other significant cities. Alexandria is the answer when the question asks for the principal urban hub rather than the protagonist's birthplace or another regional center.