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Virtue & Power

Alexander's invasion of the Persian empire

Gaugamela

The decisive battle of the Persian war, fought on ground Darius had chosen and prepared, and after which the Achaemenid empire had no field army left.

331 BCE · Near Mosul, northern Iraq; the precise site is not established

The forces, and what the figures are worth

Macedon and the League of Corinth

Alexander III · Parmenion, commanding the left

Evidence level: Probable

Macedonian troops

40,000 infantry and 7,000 cavalry

Arrian, Anabasis 3.12

Consistent with the campaign's known reinforcements and generally accepted.

The Achaemenid royal army

Darius III · Bessus, satrap of Bactria · Mazaeus

Evidence level: Literary

Persian troops

1,000,000 infantry, 40,000 cavalry, 200 scythed chariots and 15 elephants

Arrian, Anabasis 3.8

The infantry figure is rejected. The specific and modest counts of chariots and elephants in the same passage are usually accepted, which is characteristic: ancient sources are often reliable on unusual items they could count and unreliable on masses they could not.

Evidence level: Disputed

Persian troops

Between 50,000 and 120,000

Modern reconstruction

The range is wide and the disagreement genuine. What is agreed is that Alexander was substantially outnumbered and that the disparity was nothing like the ancient figures.

What happened

Darius selected a broad plain and had it levelled so that his cavalry and scythed chariots could operate freely — a rare instance of an ancient commander preparing a battlefield in advance.

Alexander advanced obliquely to his right, drawing the Persian left after him and away from the prepared ground. The manoeuvre stretched the Persian line.

The scythed chariots were dealt with by opening lanes in the infantry and letting them through to be dispatched from behind — a drill the phalanx could perform and the chariots could not counter.

A gap opened in the Persian line as its left extended. Alexander led the Companions into it in wedge and drove toward the centre. Darius again left the field. On the Macedonian left Parmenion was hard pressed and the Persian cavalry under Mazaeus broke through to the baggage camp before the collapse of the centre ended the battle.

Tactics

Gaugamela is the fullest expression of the Macedonian system and of Alexander's characteristic method: refuse the enemy the battle he has prepared, induce him to stretch his line, and drive heavy cavalry into the gap that results. The flank guards and the second line the Macedonians deployed were designed for exactly the envelopment the Persians attempted, and they held long enough for the decision to be made elsewhere.

Consequence

The Achaemenid empire lost its last field army. Babylon and Susa surrendered; Persepolis was taken and its palace burned. Darius was killed by Bessus in 330 BCE, and Alexander assumed the position of legitimate successor rather than conqueror — a claim he pursued for the rest of his life.

Location

Evidence level: Disputed

The plain of Gaugamela, near Arbela in Assyria

Modern: Near Mosul, northern Iraq; the precise site is not established

Ancient authors sometimes call it the battle of Arbela, which is some distance away. Several candidate locations on the plain have been proposed and none is confirmed by excavation.

Evidence level: Documented

Dating

1 October 331 BCE. The date is fixed unusually precisely by a lunar eclipse recorded eleven days before the battle in both the Greek sources and a Babylonian astronomical diary.

Archaeology

Evidence level: Documented

The Babylonian astronomical diaries are the significant material evidence, and they are not archaeology of the battlefield but contemporary documentary evidence from the other side. They fix the date and confirm the outcome independently of the Greek tradition. No battlefield site has been securely located.

Open questions

Evidence level: Disputed

Where was the battle fought?

The ancient sources place it at Gaugamela and sometimes at Arbela, and the two are not the same place. Candidate sites on the plain near Mosul have been proposed on topographical grounds; none has produced confirming material.

Primary sources

  • Arrian, Anabasis of Alexander 3.7-15

    The principal narrative.

  • Diodorus Siculus, Library of History 17.53-61

    An independent tradition.

  • Babylonian astronomers, Astronomical Diary for 331 BCE BM 36761 and related tablets

    A Babylonian cuneiform record noting the lunar eclipse of 20 September 331 BCE and, in a damaged passage, the defeat of the king. Independent non-Greek documentation of the campaign.

How to read the evidence labels

Evidence level: Documented
Supported by a named primary text or by excavated material evidence.
Evidence level: Probable
Supported by strong inference that most specialists accept.
Evidence level: Disputed
Substantial specialist disagreement exists; competing readings are stated.
Evidence level: Literary
Belongs to poetic or mythological construction rather than to history.
Evidence level: Mythological
Belongs to shared religious or mythic tradition rather than to any single text.
Evidence level: Unknown
The available evidence is insufficient to decide.

These labels describe the status of the evidence, not our confidence in a conclusion. A claim marked Literary is not a claim we doubt; it is a claim about what kind of thing a poem is.