Leaving 300 horse to keep the 20,000 in check, he moved on his whole line at a slow pace towards the Pinarus till it came within bow-shot of the enemy, when he gave the order to proceed at a run.

The line advanced as commanded; but before it could reach the river, the Persian horse on the extreme right, unable to restrain themselves any longer, dashed across the shallow stream, and assailed Alexander's left, where they engaged in a fierce battle with the Thessalian cavalry, in which neither attained any decided advantage.

The infantry, meanwhile, came into conflict along the rest of the line.

Alexander himself, with the right and the right-centre, charged the Asiatic troops on Darius's left, who, like their brethren at Cunaxa, instantly broke and fled.

Parmenio, with the left-centre, was less successful.