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, Aretes, with his horsemen from Alexander's second line, dashed on the Persian squadrons when their own flanks were exposed by this evolution. 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 dashed with his guard; and then pressing towards 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 gleamed nearer and nearer to him. His charioteer was struck down by a javelin at his side; and at last Darius's 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 favourably for his cause, and where his presence might have done much towards gaining a victory.