Warmatrix

The Battle of Gaugamela in 331 BCE was the last of the three great field battles that Alexander the Great fought in his campaign against the Persian empire, led by king Darius III. The Macedonians won and though Darius escaped, the power of his dynasty was broken. This was the battle that set Alexander on the throne of Persia.
Having already conquered Asia Minor, the Levant and Egypt, Alexander marched into Mesopotamia. The Persians probably planned to hold him at the banks of the river Tigris, forcing him to march southeast through a plain that had been burned to the ground, before arriving at the plain of Cunaxa hungry and desperate. Instead the Macedonian chose a northerly route, crossing the river with difficulty, though without opposition. Darius then chose a wide open battlefield near Gaugamela where he could deploy his vast army. He flattened the already flat ground even more, to ease movement of his cavalry and scythed chariots.
In the approach to the battle Alexander's general Parmenio proposed a night attack, but Alexander waved the idea off, calling it cowardly. Instead he let his army camp and personally made a reconnaissance tour of the battlefield. In the meanwhile Darius feared just such a night attack and without a good defensible camp, kept his army battle-ready throughout the night, which wore them down before the fighting had started. Alexander on the other hand is reported to have slept soundly, even with all the anxiety of the upcoming battle.
The size of the Persian army probably was somewhere between 50,000 and 100,000, including 10,000 Immortals, a large number of cavalry and light infantry, 200 chariots and 15 elephants. Darius set up his army in a long line with himself and his best troops in the center. The Macedonians fielded about 31,000 heavy infantry (phalanx, hyspaspists and allied hoplites), 9,000 light infantry and 7,000 cavalry (heavy and light), so were outnumbered roughly 2:1. Alexander deployed his heavy infantry in two lines behind each other, himself with the Companion heavy cavalry on the right and the light troops on the flanks, holding back. It seemed unavoidable that the Persians would outflank them; the light troops were ordered to deal wit that threat.
The Macedonian phalanx advanced not in a straight line, but at an angle, the left flank holding back. The Persian cavalry on the left opened the battle by attacking the Macedonian right, driving them back, however unable to break them. Next Darius launched his chariots, but the Greeks opened their ranks to let them pass, after which they were wrecked by peltasts and grooms in the rear. In the meanwhile Alexander had been creeping to the right, drawing the Persian line, which tried to counter him, slightly apart. The Macedonian phalanx pressed forward and kept the Persian infantry busy. Darius saw the Companion cavalry starting to near the edge of the ground he had prepared so well and ordered an attack. Now the time was right. Alexander launched his customary cavalry charge and broke through them, tearing into Darius' personal guard. Darius tried to recall his Greek mercenaries, but they had already advanced too far and refused to turn around. Then, like in the Battle of Issus, the Persian king panicked and ran. Alexander did not pursue, because his left flank had also come under attack and was in serious trouble, so he attacked the Persians there in the rear and had to fight fiercely to gain the upper hand. Some other Persian cavalry had exploited a gap that had opened in the Macedonian line. Instead of wheeling round and attacking their enemies in the rear, like Alexander did, they pushed for the Macedonian camp to loot it, but were beaten off by the Macedonian reserves. The last Persians standing on the battlefield were not Persians but Greek mercenaries. Alexander considered them traitors and had them cut down to the last man.
Alexander's asymmetrical deployment of his infantry was a clever tactic, no doubt inspired by the likewise asymmetrical phalanx of the Thebans. His deliberate provoking of Darius, seeking for a gap in the Persian lines through which he could attack, was a recurring theme in his battles. If one oversimplifies it can be stated that the preceding battles of Granicus and Issus were decided by aggression, but Gaugamela was a true tactical battle of maneuver. Despite that, it was again the charge of the Companions which won the battle. Yet the greatest awards should probably go to his light troops on the flanks, which despite facing superior enemies, managed to hold their ground, making the Companion charge possible in the first place.
After his third defeat and second display of cowardice, Darius's prestige was gone. His satrap Bessus murdered him, but was himself murdered by another man. Alexander went on to take Susa and Persepolis and take over the Persian empire.