The flight of the king was the signal for a general rout, so far at least as the centre and left wing of the Persian army was concerned. It was no longer a battle; it was a massacre. Alexander pressed furiously on, eager to capture the fugitive Darius. But the very completeness of his victory, it may be said, hindered him. So headlong was the flight that the dust, which, after the months of burning summer heat, lay thick upon the plain, rose like the smoke of a vast conflagration. The darkness was as the darkness of night. Nothing could be seen, but all around were heard the cries of fury and despair, the jingling of the chariot wheels, and the sound of the whips which the terrified charioteers were plying with all their might. Nor was Alexander permitted to continue the pursuit. Though the Persian left, demoralised by the cowardice of the king, had fled, the right wing had fought with better fortune. It was under the command of Mazæus, who was probably the ablest of the Persian generals, and knew how to use his superiority of numbers. Whilst the sturdy Median infantry engaged the Macedonian front line, Mazæus put himself at the head of the Parthian horse and charged the flank. Parmenio, Alexander's ablest lieutenant--his one general, as he was reported to have said--who was in command, sent an urgent request for help, so hard pressed did he find himself to be. Alexander was greatly vexed, for he saw that all chance of capturing Darius was lost, but he knew his business too well to neglect the demand. He at once called back his troops from the pursuit, and led them to the help of the left wing. Parmenio had sent the same message to that division of the phalanx which had taken part in the advance of the right wing. As things turned out, however, the help was hardly needed. On the one hand, the Thessalian cavalry had proved themselves worthy of their old reputation as the best horsemen in Greece. Held during the earlier part of the engagement in reserve, they had made a brilliant charge on the Parthians, and had restored the fortune of the day. And then, on the other hand, Mazæus and his men had felt the same infection of fear which the flight of Darius had communicated to the rest of the army. Parmenio felt the vigour of the enemy's attack languish, though he did not know the cause, and had the satisfaction of regaining, and more than regaining, the ground which he had lost, before the reinforcements arrived.