Here he drew up his forces in the order which he thought best, placing the scythed chariots in front, with supports of horse--Scythian, Bactrian, Armenian, and Cappadocian--near to them; then, the main line of battle, divided into a centre and two wings, and composed of horse and foot intermixed; and finally a reserve of Babylonians.

Sitaceni, and others, massed in heavy column in the rear.

His own post was, according to invariable Persian custom, in the centre; and about him were grouped the best troops--the Household brigade, the Melophori or Persian foot-guards, the Mardian archers, some Albanians and Carians, the entire body of Greek mercenaries, and the Indians with their elephants.
Alexander, on his side, determined to leave nothing to chance.

Advancing leisurely, resting his troops at intervals, carefully feeling his way by means of scouts, and gradually learning from the prisoners whom he took, and the deserters who came over to him, all the dispositions and preparations of the enemy, he arrived opposite the position of Darius on the ninth day after his passage of the Tigris.

His officers were eager to attack at once; but with great judgment he restrained them, gave his troops a night's rest, and obtained time to reconnoitre completely the whole position of the enemy and the arrangement which he had made of his forces.