The terms of this reply rendered further negotiation impossible.  Darius had probably not hoped much from his pacific overtures, and was therefore not greatly concerned at their rejection.  He knew that the members of his family were honorably and even kindly treated by their captor, and that, so far at any rate, Alexander had proved himself a magnanimous conqueror.  He can scarcely have thought that a lasting peace was possible between himself and his young antagonist, who had only just fleshed his maiden sword, and was naturally eager to pursue his career of conquest.  Indeed, he seems from the moment of his defeat at Issus to have looked forward to another battle as inevitable, and to have been unremitting in his efforts to collect and arm a force which might contend, with a good hope of victory, against the Macedonians.  He replaced the panoplies lost at Issus with fresh ones; he armed his forces anew with swords and spears longer than the Persians had been previously accustomed to employ, on account of the great length of the Macedonian weapons; he caused to be constructed 200 scythed chariots; he prepared spiked balls to use against his enemy’s cavalry; above all, he laid under contribution for the supply of troops all the provinces, even the most remote, of his extensive Empire, and asked and obtained important aid from allies situated beyond his borders.  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.  Leaving, therefore, the direct road to Babylon by the line of the Euphrates undefended, he selected a position which possessed all the advantages of the Mesopotamian plain, being open, level, fertile, and well supplied with water, while its vicinity to the eastern and northern provinces,