The hardy mountaineers of Affghanistan, Bokhara, Khiva, and Thibet, were then, as at present, far different from the generality of Asiatics in warlike spirit and endurance. From these districts Darius collected large bodies of admirable infantry; and the countries of the modern Kurds and Turkomans supplied, as they do now, squadrons of horsemen, strong, skilful, bold, and trained to a life of constant activity and warfare. It is not uninteresting to notice that the ancestors of our own late enemies, the Sikhs, served as allies of Darius against the Macedonians. They are spoken of in Arrian as Indians who dwelt near Bactria. They were attached to the troops of that satrapy, and their cavalry was one of the most formidable forces in the whole Persian army. Besides these picked troops, contingents also came in from the numerous other provinces that yet obeyed the Great King. Altogether, the horse are said to have been forty thousand, the scythe-bearing chariots two hundred, and the armed elephants fifteen in number. The amount of the infantry is uncertain; but the knowledge which both ancient and modern times supply of the usual character of Oriental armies, and of their populations of camp-followers, may warrant us in believing that many myriads were prepared to fight, or to encumber those who fought, for the last Darius. The position of the Persian king near Mesopotamia was chosen with great military skill. It was certain that Alexander on his return from Egypt must march northward along the Syrian coast, before he attacked the central provinces of the Persian empire. A direct eastward march from the lower part of Palestine across the great Syrian Desert was then, as now, utterly impracticable. Marching eastward from Syria, Alexander would, on crossing the Euphrates, arrive at the vast Mesopotamian plains. The wealthy capitals of the empire, Babylon, Susa, and Persepolis, would then lie to his south; and if he marched down through Mesopotamia to attack them, Darius might reasonably hope to follow the Macedonians with his immense force of cavalry, and, without even risking a pitched battle, to harass and finally overwhelm them. We may remember that three centuries afterwards a Roman army under Crassus was thus actually destroyed by the Oriental archers and horsemen in these very plains; [See Mitford.] and that the ancestors of the Parthians who thus vanquished the Roman legions, served by thousands under King Darius. If, on the contrary, Alexander should defer his march against Babylon, and first seek an encounter with the Persian army, the country on each side of the Tigris in this latitude was highly advantageous for such an army as Darius commanded; and he had close in his rear the mountainous districts of Northern Media, where he himself had in early life been satrap, where he had acquired reputation as a soldier and a general, and where he justly expected to find loyalty to his person, and a safe refuge in case of defeat.