Informed of the approach of Alexander, about the time when the Macedonian army first reached the Tigris, Darius moved from Arbêla, where his baggage and treasure were left—crossed by bridges the river Lykus or Great Zab, an operation which occupied five days—and marched to take post on the prepared ground near Gaugamela. His battle array was formed—of the Baktrians on the extreme left, under command of Bessus the satrap of Baktria; next, the Dahæ and Arachôti, under command of Barsäentes, satrap of Arachosia; then the native Persians, horse and foot alternating—the Susians, under Oxathres,—and the Kadusians. On the extreme right were the contingents of Syria both east and west of the Euphrates, under Mazæus; then the Medes, under Atropates; next, the Parthians, Sakæ, Tapyrians, and Hyrkanians, all cavalry, under Phrataphernes; then the Albanians and the Sakesinæ. Darius himself was in the centre, with the choice troops of the army near and around him—the Persian select Horse-guards, called the king’s kinsmen—the Persian foot-guards, carrying pikes with a golden apple at the butt-end—a regiment of Karians, or descendants of Karians, who had been abstracted from their homes and planted as colonists in the interior of the empire—the contingent of Mardi, good archers—and lastly, the mercenary Greeks, of number unknown, in whom Darius placed his greatest confidence. Such was the first or main line of the Persians. In the rear of it stood deep masses of Babylonians,—inhabitants of Sittakê down to the Persian Gulf—Uxians, from the territory adjoining Susiana to the east—and others in unknown multitude. In front of it were posted the scythed chariots, with small advanced bodies of cavalry—Scythians and Baktrians on the left, with one hundred chariots—Armenians and Kappadokians on the right, with fifty more—and the remaining fifty chariots in front of the centre.[374] [374] The Persian battle order here given by Arrian (iii. 11), is taken from Aristobulus, who affirmed that it was so set down in the official scheme of the battle, drawn up by the Persian officers, and afterwards captured with the baggage of Darius. Though thus authentic as far as it goes, it is not complete, even as to names—while it says nothing about numbers or depth or extent of front. Several names, of various contingents stated to have been present in the field, are not placed in the official return—thus the Sogdiani, the Arians, and the Indian mountaineers are mentioned by Arrian as having joined Darius (iii. 8); the Kossæans, by Diodorus (xvii. 59); the Sogdiani, Massagetæ, Belitæ, Kossæans, Gortyæ, Phrygians, and Kataonians, by Curtius (iv. 12).