Darius took up his position on the north bank of the River Pinarus (Deli Tschai). The centre of his line of battle was composed of 90,000 heavy-armed infantry, drawn up in three bodies of 30,000 each. One of these consisted of Greek mercenaries, and occupied the middle place; on either side were the other two—Asiatics armed in Greek fashion. His own place was behind the Greeks. It was in them that he really trusted, though he had violently resented the suggestion when it was made by another. Some weeks before, when reviewing the army with which he was about to encounter Alexander, he had asked for the opinion of Charidemus, an Athenian exile, who was in attendance on him. Charidemus was bidden to speak his mind freely, and he was imprudent enough to take the king at his word. The substance of his advice to the king was not to trust Asiatics, but to spend his accumulated treasure in hiring Greeks. Darius was deeply offended, and the great nobles about him were furious with rage. Charidemus was put to death, but his advice must have been followed. The cavalry was massed on the right wing—that end of the line which was nearest to the sea, for there alone was there any ground suit-able for their action. On the left wing, reaching far up the mountain-side, were twenty thousand light-armed infantry, who were to throw themselves on the flank of the Macedonians as soon as these should attempt to cross the river. Behind this line of battle, numbering, it is probable, not less than 120,000 men, stood a mixed multitude, swept together from all the provinces of the vast Persian Empire. This mass of combatants, if combatants they can be called, already unwieldy, received the addition of 50,000 troops, who had been posted on the southern bank of the river to cover the operation of forming the Persian line, and who were brought back when the formation was completed. The ground had been over-crowded before, and this addition to the numbers of the second line only made it more hopelessly unmanageable.

Alexander put his light infantry on the extreme right of his line, opposite, it will be remembered, to a similar force in the Persian array. Here also was the cavalry regiment of the "Companions," and with them some Thessalian horse. The main line was composed of the phalanx in five divisions, the fifth, on the extreme left, being close to the sea, which was little more than a mile and a half from the foot of the mountains—so narrow was the space which Darius had chosen for a battlefield. He could have done nothing better calculated to destroy any advantage that might have been given by his vast superiority in numbers. On the left were some squadrons of Greek cavalry, and bodies of light-armed troops from Crete and Thrace.

On coming in sight of the enemy Alexander made some changes in the disposition of his forces. The most important of these was to transfer some light infantry, cavalry, and archers to act against the 20,000 Persians who had been so placed as to threaten his right flank. It was a wise precaution, but, as a matter of fact, it was not needed. The Persians made no move, and Alexander soon perceived that they might be safely neglected. He left a few hundred cavalry to watch them, and placed the rest of the force destined for this service in his main line.

A brief time was allowed for rest when the river was reached. It was well, too, to wait for a possible forward movement on the part of the Persians. The confidence that had prompted the march to Issus might also prompt an attack. But the Persian line remained in its place, and Alexander crossed the stream. He had with him his light infantry, not slingers and archers, it should be explained, but regular soldiers, with armour and weapons so modified as to enable them to move quickly, the "Companions," and two divisions of the phalanx. The phalanx was drawn up in companies each sixteen deep. All the soldiers were armed with a pike (sarissa), which was twenty-one feet in length. The pikes of the front rank projected fifteen feet, the other end being weighted so that the weapon could be held without difficulty. The pikes of the second rank projected twelve feet, of the third, nine, of the fourth, six, of the fifth, three. The other ranks held their pikes in a slanting direction over the shoulders of those who stood in front. Alexander led the attack, as usual, in person. The Macedonians, moving as quickly as the phalanx could go, fell upon the Asiatic heavy-armed, who occupied the left division of the main Persian line. They were mainly Carduchi, the Kurds of to-day, better hands, it would seem, then as now, at plundering than at fighting. The Carduchi gave way, not waiting for the Macedonians to come to close quarters with them. Their flight endangered the safety of the king, or, rather, the king himself believed that it was endangered. He bade his charioteer turn the horses' heads and fly. As long as the ground allowed he kept to the chariot; when it became too rough he sprang upon a horse, and fled in such haste that he threw away his royal mantle, his bow, and his shield. The mixed multitude that stood behind the main line of Persian battle, as soon as they saw the king quit the field, fled, or, rather, attempted to fly. But, so narrow was the space in which they had been crowded together, they could scarcely move. A scene of frightful terror and confusion followed. The fugitives struggled fiercely with each other in the frantic attempt to escape. Had they shown as much energy in resisting the enemy as in thrusting aside and trampling down their friends, they might have changed the fortune of the day. In less than half an hour from the time when Alexander crossed the Pinarus the left wing of the Persian host was a hopeless mass of confusion.

Yet the Persians had a still unbroken strength with which much might have been done, if only there had been a leader to make use of it. The Greeks in the centre stood their ground bravely. They even advanced, charged the left divisions of the phalanx, which had not completed the passage of the Pinarus, and inflicted some loss upon it, killing as many as 150 of the front rank men, and the officer in command. But by themselves they could not hope to hold the field. When Alexander, wheeling round after his victorious assault on the Persian right, attacked them in flank, they were forced to give way. But they retired in good order, and the main body of them made good their escape. The Persian cavalry, too, had shown themselves not altogether unworthy of their ancient renown. They had actually crossed the Pinarus, and charged the Thessalian horse, which had been transferred, it should be said, by Alexander from the right to the left of his army. In the combat that ensued they held their own. But their courage failed when they became aware of the flight of Darius. When their king had given up the struggle what was there for them to stay for? To him they were bound, but they had no conception of a country to whose service it was their duty to devote their lives. They fled, suffering greatly in the pursuit.

The Macedonians lost 450 in killed, Alexander himself being slightly wounded. The slaughter among the Persians cannot be estimated. It was put down at more than 100,000. Ptolemy, afterwards King of Egypt, who was one of Alexander's most trusted generals, declared that he found a ravine so choked with dead bodies that he could use them as a bridge. Ptolemy kept a diary of the war, which he afterwards embodied in a regular narrative. Arrian, who wrote the story of Alexander's campaign in the second century of our era, had this work before him.