Battle of Issus (333 BCE): Alexander the Great vs. Darius III

By 333 BCE, Alexander had finally defeated the Achaemenid satraps of Anatolia, and at least somewhat secured his line of communication. He was now ready to march his army into the rich province of Mesopotamia and the Levant. However, the route forward took him through mountain passes that were easily defended. It was here, then, that Darius III hoped to end Alexander’s campaign. Having gathered a powerful Achaemenid army, Darius III sought to cut Alexander’s supply lines in order to force him to give battle on terms favorable to the Achaemenids. Both Alexander and Darius opted to lead their armies in person and would face each other in battle at Issus.

After defeating the field army of the Achaemenid satraps at the battle of the Granicus, Alexander turned his attention to securing the rest of Anatolia. This was critical to maintain his line of supply and communication with Greece and Macedonia.

The Achaemenid fleet was still a powerful force that the Macedonians could not hope to defeat. However, warships of the era had a critical weakness. They could only stay at sea for a limited time. They simply lacked the ability to carry enough food and water for their crews. Moreover, they had to be hauled out of the water at regular intervals or they would not be able to function. With this in mind, Alexander first secured the coastal settlements of Anatolia to reduce the Achaemenid naval bases.

With this foothold secure, Alexander moved eastwards against the cities of the Anatolian interior. Even today, Anatolia is a rugged land, and the mountain passes through which an army could move at that time were few. The sieges of the great cities of Miletus and Halicarnassus had taken several months, so as Alexander’s army approached the border between Anatolia and Syria it was already November, 333 BCE. It was at this point that Alexander began to receive reports that the Achaemenid king, Darius III was amassing an army near the Syrian town of Sochoi. In response, he dispatched a force under Parmenion to secure the coastal pass at Issus, the easiest route into Syria.

Options and Motives

Darius III was faced with a dilemma. His position on the Syrian plain favored his larger army since it gave them more room to maneuver. However, holding this large force together was expensive and winter was approaching. There were also reports of discontent among the coastal Phoenician cities that were bearing the cost of the naval war.

Attacking Parmenion’s force head on would have been difficult as the terrain favored a Macedonian defense. Darius therefore elected to march his army around Parmenion and Alexander through a more indirect route. Despite being spotted by Alexander’s scouts, Darius’ march mostly succeeded. He had not managed to place his army between Alexander and Parmenion’s forces, isolating them from each other.  Yet the Achaemenids had captured Issus, where they executed the Macedonian sick and wounded, while also cutting off Alexander’s supply lines. They were now behind the Macedonian army.

The onset of winter and the large Achaemenid army at Sochoi made the prospect of a further Macedonian advance dangerous. Alexander was convinced by his advisors to adopt a more defensive approach. The narrowness of the passes meant that any Achaemenid advance would be disorganized and disjointed. Defeating the Achaemenids in such a situation would be simple. Care had to be taken to ensure that the Achaemenids did not slip past them. Otherwise, it was possible that they might link up with the large Achaemenid naval force, and attack Alexander’s supply lines. Or even Greece itself. To avoid such predicament Alexander was forced to respond decisively when Darius and the Achaemenid army appeared to his rear. Gathering his forces, Alexander now marched backward to face Darius’ army in battle.

As with most ancient battles, estimating the size and composition of the armies was difficult. It is believed that at Issus, Alexander’s army was no larger than 40,000, though most estimates are in the 35,000-37,000 range. Alexander had found it necessary to establish garrisons in Anatolia to protect his rear, but that does not seem to have taken away much strength from his army.

Most of Alexander’s army consisted of heavy infantry who numbered somewhere around 24,000; there were 3,000 hypaspists (Alexander’s elite heavy infantry), 9,000 Macedonian phalangites, 7,000 allied hoplites, and 5,000 mercenary hoplites. These were supported by a force of 13,000 light infantry which consisted of javelin armed peltasts, archers, and slingers. Finally, Alexander had some 5,850 cavalrymen, a force that consisted of both Macedonian and allied troops.

The figures for Darius’ army are even more difficult to determine; the ancient sources give fantastical numbers ranging from 250,000 to 600,000. Modern estimates have also varied wildly but most see around 100,000 as the upper limit. An army of this size was not impossible for the period, given the resources of the Achaemenid Empire. Darius had time to assemble such a host but provisioning it in the winter would have strained his logistical capabilities, encouraging an engagement.

The core of the Achaemenid army were the elite soldiers of the Persian Immortals, who numbered around 10,000. There were also another 10,000 highly prized Greek mercenaries. The rest of the infantry were a mixture of different units, and they were also more professional than those Alexander’s Macedonians had faced at Granicus. It is believed that Darius had around 11,000 cavalrymen of different types.

Both armies deployed across the narrow pass with their flanks protected by the Gulf of Issus on one side and foothills on the other. The armies were separated by the Pinarus River, which was still an obstacle though not nearly as much as the Granicus. On their side of the river, the Achaemenids fortified the bank to make their position more defensible. Darius positioned himself at the center of the Achaemenid line with the Immortals and Greek mercenaries forming the center of his line. The rest of the infantry were deployed on either side. So large was the Achaemenid army, that a second line was formed behind the first and the Achaemenid infantry ended up spreading out into the foothills and wrapping around the Pinarus to threaten Alexander’s right flank. The Achaemenid cavalry were massed on their right flank along the shoreline.

Alexander had been forced to march to Darius to fight the battle and he deployed his troops accordingly. The heavy infantry of the phalanx was arrayed at the center of the line, while the cavalry and light infantry were split between the left and right flanks. Alexander himself led the companion cavalry on the right flank, while Parmenion was placed in overall command on the left. Since the Achaemenid line was so long that it wrapped around the river, Alexander detached a small mixed force of cavalry and infantry to protect his right flank and rear from this threat.

Interestingly, the battle began with an almost simultaneous cavalry charge by the Achaemenid cavalry on the right against Parmenion on the Macedonian left, and by Alexander on the Macedonian right against the infantry on the Achaemenid left. Initially, things did not go well for the Macedonians.

The Achaemenid cavalry outnumbered the Macedonian allied cavalry under Parmenion possibly by as many as five to one. This powerful force thundered across the Pinarus River and slammed into Parmenion’s troops forcing them backwards. It was absolutely vital that Parmenion’s troops hold their ground. If they were driven from the battlefield, then the Achaemenid cavalry would be able to strike at the exposed flanks and rear of the Macedonian phalanx. If such a thing were to occur, then it is likely that Alexander’s army would have been destroyed. However, Parmenion’s troops fought back with grim determination. Despite being driven back, they did not break and run. Instead, they launched repeated countercharges in a desperate effort to hold the Achaemenid cavalry back and buy time.

Things did not start out well for the Macedonian phalanx either. As the phalanx advanced across the river it was slowed by the Achaemenid field fortifications on the opposite bank. Then the Achaemenid Greek mercenaries launched an attack on the stalled Macedonian phalanx, driving Alexander’s men back and inflicting heavy casualties.

Writing of the battle, the historian Arrian (c.87-145 CE) claims that around 120 Macedonians “of note” were killed in the fighting. Most modern historians interpret this to mean officers. After inflicting these casualties, the Achaemenid’s Greek Mercenaries actually succeeded in pushing the Macedonian phalanx back across the Pinarus. At this point, the only bright spot for the Macedonians was that the Achaemenid troops on their side of the river in the foothills apparently had no intention of fighting.

It was now that Alexander began his attack on the Achaemenid left wing. First, his light infantry went forward and drove back their Achaemenid compatriots, sowing chaos and confusion as the Achaemenid light infantry retreated through the ranks of their spearmen. While the Achaemenids were conducting this maneuver Alexander and his cavalry charged forward.

The effect of the charge was instant and electric. Almost immediately, Achaemenid morale collapsed as they lost all cohesion. The Macedonian hypaspists now surged forward into the gap to exploit the confusion. Under this assault, the Achaemenid ranks began to disintegrate. However, there were so many soldiers packed into such a small space that they struggled both to fight and escape. Only those on the far left of the line had an escape route into the foothills. With the Achaemenid wing basically annihilated, Alexander turned his men to attack the Achaemenid center where Darius stood on his chariot commanding his troops.

Alexander’s attack relieved the pressure on the Macedonian phalanx, which surged forward to attack the Achaemenid Greek mercenaries once again. Attacked by Alexander’s cavalry as well, the mercenaries fought bravely, and Alexander received a wound on his thigh. However, Alexander now spotted Darius on his chariot and charged the Achaemenid king.

Oxyathres, brother of Darius, spotted the danger and intercepted Alexander with a squadron of his own cavalry. The fight swirled around Darius’ chariot, and Oxyathres and many of his men were killed. For a moment Alexander and Darius were face-to-face and locked eyes with each other. Darius’ chariot horses received many wounds in the course of the fighting, however, and they could not be controlled. Whether it was against his will or not, Darius was carried away from the battlefield by his uncontrollable chariot.

When the rest of the Achaemenid army noticed Darius’ flight, they abandoned their positions and fled as well. The battle was now a complete rout for the Achaemenids. As in most battles in the ancient world, the majority of the casualties were inflicted now that one side was attempting to flee. Alexander’s cavalry pursued the fleeing Achaemenids, relentlessly cutting them down as long as there was light.

Darius was forced to abandon his chariot and switch mounts in order to escape the Macedonians. The rest of the Achaemenid troops were not as lucky. According to ancient sources, the lowest estimate of the number of Achaemenid casualties resulting from the battle is around 20,000. Modern estimates generally place the Achaemenid casualties at around 20,000-40,000. Macedonian casualties, by comparison, are usually estimated at just below 5,000. It was a crushing victory for Alexander.

During the pursuit, the Macedonians also captured the Achaemenid camp and the Royal Pavilion of Darius along with it. Here they found the members of Darius’ family who had not been able to escape after the battle.

The royal women captured by the Macedonians included Darius’ wife Stateira I, his daughters Stateira II and Drypetis, and his mother Sisygambis. Alexander ordered that the royal women be treated with the utmost respect. As Alexander’s conquest of the Achaemenid empire continued they would become important tools of his reign. In 324 CE Alexander wed Stateira II, while his general and friend Hephaestion wed Drypetis; both women were later put to death on the orders of Alexander’s first wife Roxana, in 323 CE.

Following the death of her daughters, Stateira I is believed to have starved herself to death if she had not already died. Sisygambis is a particularly interesting case as she developed a genuine friendship with Alexander and treated him as her own son. For his part, Alexander honored her as his own mother. With Alexander’s death and that of her daughter and granddaughters, she starved herself to death out of grief.

Alexander’s victory was a personal triumph that opened the way to the Syrian plain for the Macedonian army. Up until this point, geography had constrained the ability of the Macedonians to enter the Achaemenid empire. Now, the path was finally clear. Alexander could march on to Mesopotamia and the Persian homeland, or strike at the riches of Egypt and Phoenicia. The strategic opportunities and options before Alexander were seemingly endless.

On the Achaemenid side, the defeat seriously curtailed their ability to resist the invaders. They still possessed exponentially greater resources, but it would take time to create a new army. In the meantime, there were no Achaemenid armies that could confront Alexander who could now march at will across the empire. Politically, the victory allowed Alexander to elevate himself over both his father and the more conservative old guard of the Macedonian kingdom.

Darius was now forced to recognize Alexander as a king, and perhaps his equal. In December of 333 BCE, Darius sent an embassy to Alexander, attempting to negotiate an end to the conflict and the return of his female relatives. Alexander was offered official recognition by the Achaemenids as both a king and an ally, along with the territory he had conquered, and a vast ransom. Many would have seized upon such a generous offer, and there are reports that Parmenion encouraged Alexander to accept. Alexander, however, refused. For many of his closest friends, advisors, and the leaders of the army, this was perhaps the first hint they would have seen of Alexander’s ambition. Before Issus, Alexander was to be king of the Greeks and Macedonians. Now he was to make himself king of Asia, and in doing so, become Alexander the Great.