The forces which he collected for the final struggle comprised--besides Persians, Medes, Babylonians, and Susianians from the centre of the Empire--Syrians from the banks of the Orontes, Armenians from the neighborhood of Ararat, Cappadocians and Albanians from the regions bordering on the Euxine, Cadusians from the Caspian, Bactrians from the Upper Oxus, Sogdians from the Jaxartes, Arachosians from Cabul, Arians from Herat, Indians from Punjab, and even Sacse from the country about Kashgar and Yarkand, on the borders of the Great Desert of Gobi.

Twenty-five nations followed the standard of the Great King, and swelled the ranks of his vast army, which amounted (according to the best authorities) to above a million of men.

Every available resource that the Empire possessed was brought into play.

Besides the three arms of cavalry, infantry, and chariots, elephants were, for perhaps the first time in the history of military science, marshalled in the battle-field, to which they added an unwonted element of grotesqueness and savagery.
The field of battle was likewise selected with great care, and artificially prepared for the encounter.

Darius, it would seem, had at last become convinced that his enemy would seek him out wherever he might happen to be, and that consequently the choice of ground rested wholly with himself.