Companion cavalry
When within missile range of the enemy, Alexander gave the order to charge. He spearheaded the assault of his heavily armed Companion cavalry, who quickly made deep cuts into the Persian left flank. The Macedonian left wing, commanded by Parmenion, was meanwhile driven back by Nabarsanes' large cavalry. The Macedonians' central phalanx crossed the river and clashed with the renegade Greek mercenaries who fronted Darius' vanguard. As the Companion cavalry pushed further into the Persian left, the danger arose that Darius would exploit the gap that had formed between Alexander and the rest of his army. When he was satisfied that the left wing was crippled and no longer a threat, Alexander remedied the situation by moving the Companions to assault the Persian centre in the flank. Unable to handle the added pressure, the Persian vanguard was forced to withdraw from the river bank, allowing the Macedonian phalanx to continue their advance and lifting the pressure on Parmenion's left wing.