Battle of Gaugamela

Battle of Gaugamela, (October 1, 331 bce) clash between the forces of Alexander the Great of Macedonia and Darius III of Persia that decided the fate of the Persian Achaemenian Empire.

Alexander’s invasion of Persia

From his accession in 336 bce at age 20, Alexander had set his mind on the conquest of Persia. Indeed, he had grown up to the idea. Moreover, he needed the wealth of Persia if he was to maintain the army built by his father, Philip II, and pay off the debts he owed. The exploits of the Ten Thousand, Greek soldiers of fortune, and of Agesilaus of Sparta, in successfully campaigning in Persian territory had revealed the vulnerability of the Achaemenian Empire. With a good cavalry force, Alexander could expect to defeat any Persian army, and the Macedonian Hetairoi (“Companion”) cavalry were arguably the finest equestrian unit in the ancient world. In the spring of 334 Alexander crossed the Dardanelles, leaving Antipater, who had already faithfully served Alexander’s father, as his deputy in Europe with more than 13,000 troops. Alexander himself commanded about 30,000 infantry and more than 5,000 cavalry, of whom nearly 14,000 were Macedonians and about 7,000 were allies sent by the Greek League. This army was to prove remarkable for its balanced combination of arms. Much work fell on the lightly armed Cretan and Macedonian archers, Thracian peltasts (light infantry equipped with a pelta, or hide-covered wicker shield, and spear), and Agrianian javelineers. In pitched battle the striking force was the cavalry, and the core of the army—should the issue still remain undecided after the cavalry charge—was the phalanx, 9,000 heavy infantry armed with 13-foot (4-meter) spears and shields, and the 3,000 men of the royal battalions, the hypaspists (shield bearers).

Alexander’s second in command was Parmenio, who had secured a foothold in Asia Minor during Philip’s lifetime. Many of his family and supporters were entrenched in positions of responsibility. The army was accompanied by surveyors, engineers, architects, scientists, court officials, and historians. From the outset, Alexander seems to have envisaged an unlimited operation. In the spring of 331 Alexander could at last leave the Mediterranean to strike into the heart of the Achaemenian Empire, for his occupation of the coasts had triggered the collapse of Persia’s command of the sea. After his conquest of Egypt, he returned through Syria, stopped at Tyre to make final arrangements for the conquered provinces, traversed Mesopotamia, and reached the Tigris River some four days’ march above the site of Nineveh. The coincidence of a lunar eclipse gives the exact day—September 20, 331—upon which the Macedonian army crossed the Tigris.

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Disposition of forces and the Battle of Gaugamela

The plain of Gaugamela, northeast of Nineveh (across the Tigris from what is now Mosul, Iraq), was chosen by Darius for a battle with Alexander’s advancing force because of its suitability for Darius’s cavalry, which outnumbered Alexander’s. The total troop strengths given by ancient authorities vary, some being quite fantastic, but, in any case, the Persians outnumbered the Macedonians. In front of the Persian line were the scythed war chariots, 50 on the right and center, 100 on the left; Darius had leveled the plain ahead to give them a clear run. Darius himself was in the center of the line, with the Greek mercenary and Persian heavy infantry, archers, and Persian and Indian cavalry. On the left wing was Bessus, satrap of Bactria, with Bactrian, Scythian, and Arachosian cavalry. Mazaeus, formerly satrap of Cilicia, was on the right wing, with Armenian and Cappadocian cavalry. Inferior troops extended the line between center and wings. Alexander was thus faced with the problem of striking a decisive blow with his heavy infantry and cavalry without being enveloped by the cavalry of the Persian wings or letting the chariots cut up the phalanx.

Alexander took up position on his right wing, heading the Companion cavalry. In front of him were half the archers and Agrianian javelineers to deal with the chariots. Left of the Companion cavalry were the hypaspists and then the heavy infantry phalanx in six battalions. The left wing was composed of Greek and Thessalian cavalry commanded by Parmenio. Because of the danger of encirclement, a second infantry line was formed, prepared to face about if necessary, and reserves were placed on each wing at an angle so that they could either extend the line or double back to meet a flank attack. The right reserve consisted of Greek mercenary and Paeonian cavalry and lancers (prodromoi), supported by the other half of the archers and Agrianians and veteran mercenaries; the left reserve was composed of Greek and Thracian cavalry. Well behind the army, the Thracian infantry guarded the camp where the baggage and prisoners, including Darius’s family (who had been captured after the Persian rout at Issus), had been left.

Alexander led en echelon toward the right, away from the leveled ground. Bessus sent out successive troops of Scythian and Bactrian cavalry. The mercenary cavalry engaged them, supported subsequently by the Paeonians, and, though outnumbered, they stood their ground. Meanwhile, before the phalanx could get clear of the leveled ground, Darius sent out the chariots, but the javelineers and archers shot down most of the charioteers before they reached the infantry, who opened ranks to let the others pass through. Having ordered the lancers to charge the Scythians and Bactrians, Alexander continued to advance to the right. As more of the Persian left was engaged, a gap opened in the Persian left center. Alexander promptly wheeled left with the Companion cavalry, hypaspists and four phalanx battalions in a charge at the gap. The Persian center soon broke, and Darius led the flight.

Pursuit was halted by a call for help from Parmenio. Mazaeus’s cavalry had attacked the Thessalians, and the other two phalanx battalions had halted to support them. Persian and Indian cavalry had ridden through the gap thus made in the phalanx and on to the camp. The second infantry line had, however, turned and attacked them from the rear. The retreating Persians and Indians collided with Alexander’s relieving force and were driven off after a sharp fight, by which time the Thessalians had also scattered their opponents. Persian losses were heavy. Arrian gives the Macedonian dead as 100, although Diodorus and Quintus Curtius give higher figures. Darius fled to Bactria, and he was assassinated by Bessus in 330. The Macedonian victory spelled the end of the Achaemenian Empire founded by Cyrus II (the Great) and left Alexander the master of Southwest Asia.

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