In the 4th century BCE, Alexander the Great conquered the Achaemenid Persian Empire, reshaping the political and economic landscape of the ancient Near East. Historical sources describe his return journey from the Indus Valley to Mesopotamia, where he planned to travel by water from Susa to Babylon. During this journey, Alexander recognized a strategic problem: heavy sedimentation in southern Mesopotamia was gradually pushing the coastline of the Persian Gulf farther south, making existing harbors unusable.
To solve this, Alexander founded a new port city—Alexandria on the Tigris—near the confluence of the Tigris River and the Karun River, approximately 1.8 kilometers from the ancient coastline. Later known as Charax Spasinou or Charax Maishan, the city was mentioned by Roman authors and referenced in inscriptions found as far away as Palmyra in Syria. Despite these clues, its exact location remained uncertain for centuries.