The effect of this oblique movement was to bring the phalanx and his own wing nearly beyond the limits of the ground which the Persians had prepared for the operations of the chariots; and Darius, fearing to lose the benefit of this arm against the most important parts of the Macedonian force, ordered the Scythian and Bactrian cavalry, who were drawn up in advance on his extreme left, to charge round upon Alexander's right wing, and check its farther lateral progress. Against these assailants Alexander sent from his second line Menidas' cavalry. As these proved too few to make head against the enemy, he ordered Ariston also from the second line with his right horse, and Cleander with his foot, in support of Menidas.
The Bactrians and Scythians now began to give way; but Darius reenforced them by the mass of Bactrian cavalry from his main line, and an obstinate cavalry fight now took place. The Bactrians and Scythians were numerous, and were better armed than the horsemen under Menidas and Ariston; and the loss at first was heaviest on the Macedonian side. But still the European cavalry stood the charge of the Asiatics, and at last, by their superior discipline, and by acting in squadrons that supported each other,[[52]] instead of fighting in a confused mass like the barbarians, the Macedonians broke their adversaries and drove them off the field.
[!-- Note Anchor 52 --][Footnote 52: The best explanation of this may be found in Napoleon's account of the cavalry fights between the French and the mamelukes: "Two mamelukes were able to make head against three Frenchmen, because they were better armed, better mounted, and better trained; they had two pair of pistols, a blunderbuss, a carbine, a helmet with a visor, and a coat of mail; they had several horses, and several attendants on foot. One hundred cuirassiers, however, were not afraid of one hundred mamelukes; three hundred could beat an equal number, and one thousand could easily put to the rout fifteen hundred, so great is the influence of tactics, order, and evolutions! Leclerc and Lasalle presented their men to the mamelukes in several lines. When the Arabs were on the point of overwhelming the first, the second came to its assistance on the right and left; the mamelukes then halted and wheeled, in order to turn the wings of this new line; this moment was always seized upon to charge them, and they were uniformly broken.">[
Darius now directed the scythe-armed chariots to be driven against Alexander's horse-guards and the phalanx, and these formidable vehicles were accordingly sent rattling across the plain, against the Macedonian line. When we remember the alarm which the war chariots of the Britons created among Cæsar's legions, we shall not be prone to deride this arm of ancient warfare as always useless. The object of the chariots was to create unsteadiness in the ranks against which they were driven, and squadrons of cavalry followed close upon them to profit by such disorder. But the Asiatic chariots were rendered ineffective at Arbela by the light-armed troops, whom Alexander had specially appointed for the service, and who, wounding the horses and drivers with their missile weapons, and running alongside so as to cut the traces or seize the reins, marred the intended charge; and the few chariots that reached the phalanx passed harmlessly through the internals which the spearmen opened for them, and were easily captured in the rear.
A mass of the Asiatic cavalry was now, for the second time, collected against Alexander's extreme right, and moved round it, with the view of gaining the flank of his army. At the critical moment, when their own flanks were exposed by this evolution, Aretes dashed on the Persian squadrons with his horsemen from Alexander's second line. While Alexander thus met and baffled all the flanking attacks of the enemy with troops brought up from his second line, he kept his own horse-guards and the rest of the front line of his wing fresh, and ready to take advantage of the first opportunity for striking a decisive blow.
This soon came. A large body of horse, who were posted on the Persian left wing nearest to the centre, quitted their station, and rode off to help their comrades in the cavalry fight that still was going on at the extreme right of Alexander's wing against the detachments from his second line. This made a huge gap in the Persian array, and into this space Alexander instantly charged with his guard and all the cavalry of his wing; and then, pressing toward his left, he soon began to make havoc in the left flank of the Persian centre. The shield-bearing infantry now charged also among the reeling masses of the Asiatics; and five of the brigades of the phalanx, with the irresistible might of their sarissas, bore down the Greek mercenaries of Darius, and dug their way through the Persian centre.
In the early part of the battle Darius had showed skill and energy; and he now, for some time, encouraged his men, by voice and example, to keep firm. But the lances of Alexander's cavalry and the pikes of the phalanx now pressed nearer and nearer to him. His charioteer was struck down by a javelin at his side; and at last Darius' nerve failed him, and, descending from his chariot, he mounted on a fleet horse and galloped from the plain, regardless of the state of the battle in other parts of the field, where matters were going on much more favorably for his cause, and where his presence might have done much toward gaining a victory.
Alexander's operations with his right and centre had exposed his left to an immensely preponderating force of the enemy. Parmenio kept out of action as long as possible; but Mazaeus, who commanded the Persian right wing, advanced against him, completely outflanked him, and pressed him severely with reiterated charges by superior numbers.
Seeing the distress of Parmenio's wing, Simmias, who commanded the sixth brigade of the phalanx, which was next to the left wing, did not advance with the other brigades in the great charge upon the Persian centre, but kept back to cover Parmenio's troops on their right flank, as otherwise they would have been completely surrounded and cut off from the rest of the Macedonian army. By so doing, Simmias had unavoidably opened a gap in the Macedonian left centre; and a large column of Indian and Persian horse, from the Persian right centre, had galloped forward through this interval, and right through the troops of the Macedonian second line. Instead of then wheeling round upon Parmenio, or upon the rear of Alexander's conquering wing, the Indian and Persian cavalry rode straight on to the Macedonian camp, overpowered the Thracians who were left in charge of it, and began to plunder. This was stopped by the phalangite troops of the second line, who, after the enemy's horsemen had rushed by them, faced about, countermarched upon the camp, killed many of the Indians and Persians in the act of plundering, and forced the rest to ride off again.
Just at this crisis, Alexander had been recalled from his pursuit of Darius by tidings of the distress of Parmenio and of his inability to bear up any longer against the hot attacks of Mazaeus. Taking his horse-guards with him, Alexander rode toward the part of the field where his left wing was fighting; but on his way thither he encountered the Persian and Indian cavalry on their return from his camp.