331 BC

Battle of Gaugamela

Alexander defeats Darius III at Gaugamela

Eleven days before the battle, a lunar eclipse was read as foretelling Darius's defeat. Persian troops who broke through to Alexander's camp stopped to plunder instead of striking his army from behind.

1 October 331 BC: the gap in the Persian line

On 1 October 331 BC — a date strongly supported by Babylonian astronomical evidence — Alexander's Macedonian-led army met the Achaemenid army of Darius III near Gaugamela, east of the Tigris in the district of Arbela. Darius had selected and flattened an open plain to suit his cavalry and scythed chariots; Alexander answered by moving his right wing obliquely toward the edge of that prepared ground.

Persian cavalry movements opened a gap near the center. Through it, Alexander's cavalry wedge and the Macedonian phalanx attacked toward Darius, while Parmenion's left wing — with the Thessalian cavalry — held through heavy fighting. Darius fled; Alexander pursued until nightfall and still failed to catch him.

Numbers to trust and numbers to discard

Arrian credits Alexander with about 40,000 infantry and 7,000 cavalry. On the Persian side, no reliable total can be recovered — specialist scholarship calls the ancient figures, ranging from 200,000 to a million infantry, worthless.

Even the battlefield is only approximately known: Gaugamela lay roughly sixty miles from Arbela, probably east of Mosul, and the proposed sites around the Jomel River remain hypotheses.

The road to Babylon, not yet the end of an empire

The remaining Achaemenid field army disintegrated, leaving Babylon and Susa exposed as Darius retreated toward Ecbatana. Twenty days after the battle, Mazaeus — who had commanded the Persian right — surrendered Babylon to Alexander and was appointed its satrap.

The old title's 'effectively ending' overstates the day: Darius survived, resistance continued, and major campaigning ran through 330 BC and beyond, with Darius killed during his eastward flight that year.

Sources

Researched 23 Aug 2026 5 sources 3 audit passes Date corrected

How this was checked

Researched from the web into a fact sheet, rewritten from that sheet, then audited against it by a different model. How the pipeline works →

Date corrected. The research places this at -0331-10-01.

What the sources leave uncertain

The date, once debated, is strongly supported by Babylonian astronomical evidence and the lunar eclipse chronology.
The exact battlefield location cannot be recovered securely; proposed sites around the Jomel River east of Mosul remain hypotheses.
Ancient accounts obscure important tactical details and give irreconcilable Persian troop and casualty figures.
The surviving Greek and Roman narrative sources differ over Darius’s peace offers, including whether the ransom was 10,000 or 30,000 talents.