Alexandria is the largest explorable historical city in Assassin’s Creed Origins.
The game portrays Alexandria as a major Mediterranean center during the final years of the Ptolemaic Kingdom. Its districts include dense streets, monumental architecture, waterfront areas, markets, and the Great Library setting. Bayek’s investigations there connect local events to the court of Ptolemy XIII and the political struggles involving Cleopatra and Julius Caesar.
Alexandria differs from the game’s other large locations because of its urban density and strong Hellenistic character. Memphis is another major city, while Cyrene and Siwa provide different regional environments. The Egyptian world map also includes deserts, villages, tombs, military outposts, and the Nile Valley.
The question concerns the explorable city in the game, not the largest city in ancient Egypt at every point in history. Origins is a historical-fiction reconstruction rather than a complete archaeological survey, so its map scale and boundaries are designed for gameplay.