Conquest of Persia, 331–330 B.C.

From Egypt Alexander marched north to Damascus and crossed Mesopotamia on his way through the heart of the Persian Empire. Darius, after his defeat at Issus, had escaped to Babylon, where he assembled a great new force. Moving north to Arbela (Erbil), he took his stand on the nearby plains of Gaugamela. Alexander routed the enemy forces, but the Persian ruler once again escaped. Claiming that Darius had abdicated, Alexander declared himself Great King of the Persian Empire.

The Macedonian army followed the Tigris River to Babylon and continued on to the ancient Persian capitals of Susa, Persepolis, and Ecbatana. From each conquered city it collected rich spoils. Darius retreated eastward until he was killed by a kinsman, Bessus, who tried unsuccessfully to halt the Macedonian advance.