Darius, meanwhile, was in no position to interrupt this series of successes in Syria and in Egypt. He had no army there prepared to take the field, but he did try to interfere with the Greek lines of communication in regions more remote from the present scene of operations. Antigonus, left in Phrygia as its governor, was attacked by a force composed of some of the soldiers who had fought on the Persian side at Issus, as well as of contingents from Cappadocia and Paphlagonia. But the attempt was unsuccessful. Antigonus showed remarkable military ability, for with his small force he defeated the Persians and added to the region under him the country of Lycaonia, which had never submitted to Persian rule. In the spring of 331 Alexander left Egypt for his march to the interior of the Persian Empire, and by the middle of the summer he crossed the Euphrates near Thapsacus, and from there, taking a northerly direction through Mesopotamia, he passed the Tigris on the 20th of September.
The advance of the Greek army was continuous, little resistance being offered to its progress. It seemed to be the aim of Darius to do nothing to prevent Alexander from penetrating into the interior. If the Greeks were defeated there, they would be cut off from retreat, and in case the Persians again failed, there would be a chance for the vanquished to withdraw in security to the mountainous country to the north. Alexander has been criticised for delaying so long in his occupation of Syria and Egypt; indeed Parmenio had urged him to accept the terms offered by Darius after the battle of Issus, a suggestion which called forth from Alexander the reply “that he would do it if he were Parmenio.” But the small number of soldiers under his command showed the strategy he followed to be as cautious as his conduct of the expedition was daring. If he had gone straight on after the battle of Issus, he would have been obliged to detach enough men from his main army to act as a corps of observation in Syria and Egypt, and this would have left him hardly more than 20,000 men.
In the meantime he had received accessions of numbers, so that when he came to confront Darius for the second time he had under his command about 47,000 men. The engagement took place at Gaugamela (October, 331 B.C.), not far from the ruins of Nineveh. Darius had made some attempt to give an improved armament to his foot soldiers, supplying them with longer spears and swords so that they might fight the Macedonian phalanx on more equal terms. Besides this, he had provided chariots armed with scythes and a small number of elephants, which could be effectively used only in a level country. But his chief hope lay in his cavalry, of which he probably had 12,000, while Alexander had but 7000.
The Greeks had had four days’ rest in a fortified camp before they were drawn up in battle array, and besides this the ground between them and the Persians had been carefully reconnoitered, in order to discern if the enemy had constructed concealed pits to confuse the cavalry charge. There was no way of protecting the flanks of the army, so Alexander placed a reserve force behind with orders to move towards the right or the left, according as the expected turning movement from the Persians might develop. The Greeks moved forward on the 30th of September, with Alexander leading the Macedonian heavy cavalry and the bulk of the phalanx. He directed his attack against the enemy’s left wing, but as he did so he was charged on the flank by the Scythian and Bactrian horse. He sent against them the reserves previously mentioned, and himself engaged the Persian infantry, who had lost heart when they were attacked by the Macedonian cavalry. The manœuvers with the scythe-bearing chariots did no damage, for the Greeks made way for them to pass through their ranks, and re-formed again as soon as they had rattled past. The onslaught of the phalanx proved irresistible; the Asiatic foot could not withstand its superior armament and discipline. The Persian center was broken and again Darius had the ignominious experience of a headlong flight. The Persian cavalry, left to battle alone, was soon demoralized and could not hold its ground.
Parmenio’s experience with the left wing of the Greeks was different, for he had difficulty in keeping his position against the Persian horse. He could not follow Alexander’s advance, and hence there came to be a great gap between the two positions of the army. In this open space the Persians precipitated themselves; the Greek lines in battle array were forced farther apart and their camp occupied. It was a most dangerous position, but the barbarians, instead of using their advantage, busied themselves in plundering the Greek camp. Alexander turned from pursuing the Persian center to help the hard-pressed left wing, and on his way met the enemy’s cavalry, now on their way back with the booty of the Macedonian camp. He tried to cut them off from their main body, but they fought with desperation and succeeded in breaking through. In the hand-to-hand fights one of Alexander’s closest friends, Hephæstion, was wounded.
The danger to the left wing was now over, for the Persian commander Mazæus, on hearing of his king’s flight, had ceased the attack on Parmenio, who now occupied the Persian camp, while Alexander resumed the pursuit of the main body, anxious to get Darius into his hands. He marched with great rapidity, reaching on the day after the battle Arbela, at which place the supplies and treasures of the flying Persians were discovered. But the Great King had made good his escape to Media, where, owing to the mountainous character of the country, it was useless to pursue him farther. The results of the battle were impressive materially and emotionally. The Persians had no heart to continue the war. Their army was destroyed, 10,000 prisoners were in the hands of their enemy, and the road to their capitals, Babylon and Susa, lay open. All this had been won by Alexander at a small cost, only 100 Macedonians having fallen, and the whole loss of the Greek army did not exceed 500 men.
Alexander marched to Babylon, which was surrendered without resistance by its inhabitants, who welcomed him as a liberator. Religious differences had made the citizens regard the Persians as oppressors, and Alexander won over the Babylonians by acting as the protector of their national religion. He rebuilt the Babylonian temples and also showed a placable temper by keeping the Persian Mazæus as satrap of the province of Babylonia. Without delaying at Babylon longer than was necessary to conciliate the inhabitants, Alexander passed to Susa. Its citadel offered no resistance, and with its surrender the town and its treasury, amounting to 50,000 talents ($60,000,000), became the property of the conqueror. (December, 331 B.C.)
The next stage of the conquest of the interior of Asia was the occupation of the country called Persis, the homeland of the Persians. To reach it a difficult country held by Uxian hillmen had to be passed. These were proud of their independence, for they had never paid tribute to the Persians, and they now occupied their mountain defile, prepared to dispute the passage of the Greeks. They were easily circumvented by Alexander’s strategy, and brought to reason. Farther on, the access to Persepolis was strongly defended by the Persians, but Alexander forced his way through devious mountain roads and took the capital without trouble. The national treasure, equivalent to 120,000 talents, fell into his hands.
Up to this point the march of Alexander had been through territories which the Persians had themselves acquired by conquest, and which had been long exploited by their satraps. The populations were, therefore, not inimical to the new conquerors. Indeed, as we have seen in many cases, the latter were greeted as deliverers from the heavy yoke of the Persians. On its side, the Macedonian army had been kept under strict discipline, and the lives and property of the people through whom it had passed were carefully respected. But Persepolis was really in the enemy’s country, the cradle of Persian rule, and there was no chance of reconciling its inhabitants by kind treatment. They were now to feel the brunt of real warfare. The city was given up to plunder, and the royal citadel of the Achæmenian kings was burnt down in a drunken revel. This ruthless act has been condemned, and it does appear to have been the result of a moment of excess, not planned as part of a policy of repression, for Alexander ordered the flames quenched, though he himself had cast the first firebrand that had set the costly cedar work of the palace in flames.
These various military operations lasted far into the autumn. When winter came the sorely tried and traveled Greeks took four months’ rest, and from this point begins another stage in the expedition, for Persis was regarded as sufficiently pacified to allow the bulk of the army to march into Media. Here Darius was preparing to make a last stand, but his efforts to collect a new army had the somewhat pitiful result of bringing to his standard a force of not more than 3000 horsemen and 6000 foot soldiers. As the Greeks approached, he fled before them, recognizing the hopelessness of resistance. He seemed minded to take refuge in the extreme limits of what had been his empire, the province of Bactria. Without striking a blow, Alexander occupied Ecbatana, the last of the great Persian capitals.