The Persians, in fact, expected, and were prepared to meet a night attack. Such was the apprehension that Darius entertained of it, that he formed his troops at evening in order of battle, and kept them under arms all night. The effect of this was that the morning found them jaded and dispirited, while it brought their adversaries all fresh and vigorous against them.
The written order of battle which Darius himself caused to be drawn up, fell into the hands of the Macedonians after the engagement, and Aristobulus copied it into his journal. We thus possess, through Arrian, unusually authentic information as to the composition and arrangement of the Persian army. On the extreme left were the Bactrian, Daan, and Arachosian cavalry. Next to these Darius placed the troops from Persia proper, both horse and foot. Then came the Susians, and next to these the Cadusians. These forces made up the left wing. Darius's own station was in the centre. This was composed of the Indians, the Carians, the Mardian archers, and the division of Persians who were distinguished by the golden apples that formed the knobs of their spears. Here also were stationed the body-guard of the Persian nobility. Besides these, there were, in the centre, formed in deep order, the Uxian and Babylonian troops, and