In the early summer of 331, Alexander the Great took his whole army northeast through Syria, reaching the Euphrates, not earlier than July 10. Darius, the great king of the Persian empire, knew very well that Babylon itself was Alexander’s next objective. Babylon, the great city on the Lower Euphrates, was the economic center of the empire.
Alexander the Great struck hard, fast, and with maximum economy. It was therfore that he would come straight down the east bank of the Euphrates, just as the Cyrus had done in 401, to meet disastrous defeat at Cunaxa. It was quite noticeable that Darius had studied the battle of Cunaxa with some care, and hoped to repeat it in detail. The plain at Cunaxa, some sixty miles north-west of Babylon, was ideal for calvary maneuvers-and the Great King now had some 34,000 armed horsemen at his disposal. After a quick change in strategy the Great King decided to try and hold Alexander at the Tigris. It was a bold and risky plan since no one could be sure where he might pop up.
The Macedonians reached Abu Wajnam on September 18 and encountered no opposition. A few frightened scouts fled the area with the news to the Great King who was across the Greater Zab and approaching Mosul. Darius was forced to change his plans again. He no longer had the Tigris Between them. His best chance to locate another open plain suitable for cavalry and chariot maneuvers and to bring Alexander to battle there. His scouts found Gaugamel, a village between the Khazir river and the ruins of Nineveh. Darius brought up his troops, saw the plain and sent sapper to clear it. What he unfortunately did not do was to occupy the low hills some 3 miles to northwest. Where Alexander’s own scouts were able to observe everything he did. (Microsoft Encarta)
After crossing the Tigris, Alexander made contact with a regiment of Mazaeus’ calvary. The mounted soldiers of Paeoniar where then sent to deal with this problem. The Persians fled; Ariston speared their colonel and presented his head to the King. The Macedonians then got 48 hours of rest. Four days later Aristons calvary was sighted again. This could indicate the entire army. A quick calvary raid led by Alexander took a few prisoners. The prisoners then told him what he wanted to know. Darius now lay eight miles beyond the hills. His ground leading operations indicated that he didn’t plan on moving anytime soon. Alexander then gave his troops another four days rest. The heat was grueling and Alexander wanted his men fresh for the coming battle.
During this time Darius agents tried to smuggle in letters saying that Alexander’s men should kill him. These were intercepted and destroyed. The camp was also protected by a ditch and a palisade. It was now that Darius for a third time attempted to settle things with Alexander peacefully. This time he offered all territories west bound of the Euphrates, and 3000 talons ransom for his mother and daughter as well. He also offered the hand of one daughter in marriage, as well as the retentions of Ochus as a permanent hostage. Alexander’s war council thought he should accept the idea.
Darius had 34,000 armed calvary to Alexander’s 7,250 calvary and not strategy could get round that basic fact (Mcbride and Sekunda 27). Alexander was going to be outflanked and knew it. There were no mountains or seas to protect his flanks here as in previous battles. Darius’ left flank line overlapped Alexander’s by a mile. So while Alexander’s basic order of battle remained unchanged, he took special tasks to protect his rear and also make his calvary line look weaker than it was. He stationed a powerful force of mercenaries on his right wing carefully masking them with calvary squadrons. He pulled both flanks back 45 degrees from his main battle line. Finally he placed the lead infantry and the rest of the Greek mercenaries to cover his rear.
He was truly making a virtue of necessity. Alone in his tent he thought of a great battle plan which was to be used again centuries later by Napoleon. To reduce the odds against him and to create an opening for his charge, he planned to draw as many of Darius’ calvary as possible away from the center and into his flank guards. When the flanks were committed, he would strike the center. So on September 30th, 331 the Macedonians and the Persian armies moved forward into an engagement which could secure the whole Persian Empire (Green 50). It was Alexander’s military masterpiece both in design and execution. The Macedonians advanced with the left wing back trying to lure the Persian right into premature flank engagement. At the same time the Persian left-outflanked Alexander so much that Darius’ calvary commander and the calvary were almost opposite the Persian headquarters command post.
Subsequently, neither side wanted to fight first, but Darius finally did act first. Trying to halt this drift on his left flank toward dangerous ground, he ordered an attack on Alexander’s right wing. This was the move Alexander was waiting for. Once the calvary was engaged, Alexander fed in further units from his flank guard. To stop this increasing pressure, Darius calvary commander brought up more men to penetrate for roll up Alexander’s flank. He was most likely still unaware of the 6000 mercenaries behind the calvary. A point came when Alexander’s calvary, which numbered no more than 1100, was holding nearly ten times its own strength of front-line Persian horsemen (Microsoft Encarta). Meanwhile Darius launched his chariots. They were very useless. Alexander’s screen of light armored troops in front of the main line slaughtered the horses with javelins and stabbed the drivers as they went past. The well-drilled ranks of the rear phalanx opened wide, and Alexander’s grooms rounded up the survivors.
Gathering his remaining forces in a wedge he charged, Alexander knew it was now or never! In a total of three minutes the whole course of the battle was changed. Bessus, still fully engaged against Alexander’s right, found his own flank dangerously exposed by Alexander’s charge.
Alexander was very frustrated that he couldn’t find a way to kill Darius. The Achaemenid empire had split in two, and its ruler’s authority ripped to shreds, but Alexander was still full of intelligence that he could still proclaim himself the Great King in Darius’ place without anyone there to stop him. It is told that later Darius fled away and was killed by Alexander.
Alexander intelligence soon pieced together the story of the Great King’s escape. He and his retinue had fled headlong to Arbela, not even bothering to break the river bridges as they went. Here they were joined by Bessus and the Bactrian cavalry, 2000 loyal Greek mercenaries, and a few survivors from the royal guard. Soon after midnight these battered remnants of the Persian grand army set out from Arbela, taking the road east though the Armenian mountains, and eventually hitting Ecbatana from the north. Here Darius stopped for a while to let some stragglers join up. He made a few efforts to reorganize and rearm them and also sent a few nervous notes to his governors and generals in Bactria and the upper satrapies urging them to remain loyal. But at Gaugamela he lost his nerve and never recovered it (Green 75).