Darius, informed that Alexander was approaching, resolved to fight where he was encamped, behind the river Pinarus. He, however, threw across the river a force of 30,000 cavalry, and 20,000 infantry, to ensure the undisturbed formation of his main force behind the river.[274] He composed his phalanx or main line of battle, of 90,000 hoplites; 30,000 Greek hoplites in the centre, and 30,000 Asiatics armed as hoplites (called Kardakes), on each side of these Greeks. These men—not distributed into separate divisions, but grouped in one body or multitude[275]—filled the breadth between the mountains and the sea. On the mountains to his left, he placed a body of 20,000 men, intended to act against the right flank and rear of Alexander. But for the great numerical mass of his vast host, he could find no room to act; accordingly they remained useless in the rear of his Greek and Asiatic hoplites, yet not formed into any body of reserve, or kept disposable for assisting in case of need. When his line was thoroughly formed, he recalled to the left bank of the Pinarus the 30,000 cavalry and 20,000 infantry which he had sent across as a protecting force. A part of this cavalry were sent to his extreme left wing, but the mountain ground was found unsuitable for them to act, so that they were forced to cross the right wing, where accordingly the great mass of the Persian cavalry became assembled. Darius himself in his chariot was in the centre of the line, behind the Grecian hoplites. In the front of his whole line ran the river or rivulet Pinarus; the banks of which, in many parts naturally steep, he obstructed in some places by embankments.[276] [274] Compare Kallisthenes ap. Polyb. xii. 17.; and Arrian, ii. 8, 8. Considering how narrow the space was, such numerous bodies as these 30,000 horse and 20,000 foot must have found little facility in moving. Kallisthenes did not notice them, as far as we can collect from Polybius. [275] Arrian, ii. 8, 9. Τοσούτους γὰρ ~ἐπὶ φάλαγγος ἁπλῆς~ ἐδέχετο τὸ χωρίον, ἵνα ἐτάσσοντο. The depth of this single phalanx is not given, nor do we know the exact width of the ground which it occupied. Assuming a depth of sixteen, and one pace in breadth to each soldier, 4000 men would stand in the breadth of a stadium of 250 paces; and therefore 80,000 men in a breadth of twenty stadia (see the calculation of Rüstow and Köchly, p. 280, about the Macedonian line). Assuming a depth of twenty-six, 6500 men would stand in the stadium, and therefore 90,000 in a total breadth of 14 stadia, which is that given by Kallisthenes. But there must have been intervals left, greater or less, we know not how many; the covering detachments, which had been thrown out before the river Pinarus, must have found some means of passing through to the rear, when recalled.