At Ekbatana Alexander was joined by a fresh force of 6000 Grecian mercenaries,[435] who had marched from Kilikia into the interior, probably crossing the Euphrates and Tigris at the same points as Alexander himself had crossed. Hence he was enabled the better to dismiss his Thessalian cavalry, with other Greeks who had been serving during his four years of Asiatic war, and who now wished to go home.[436] He distributed among them the sum of 2000 talents in addition to their full pay, and gave them the price of their horses, which they sold before departure. The operations which he was now about to commence against the eastern territories of Persia were not against regular armies, but against flying corps and distinct native tribes, relying for defence chiefly on the difficulties which mountains, deserts, privation, or mere distance, would throw in the way of an assailant. For these purposes he required an increased number of light troops, and was obliged to impose even upon his heavy-armed cavalry the most rapid and fatiguing marches, such as none but his Macedonian Companions would have been contented to execute; moreover he was called upon to act less with large masses, and more with small and broken divisions. He now therefore for the first time established a regular Taxis, or division of horse-bowmen.[437] [435] Curtius, v. 23, 12. [436] Arrian, iii. 19, 10: compare v. 27, 7. [437] Arrian, iii. 24, 1. ἤδη γὰρ αὐτῷ καὶ ἱππακοντισταὶ ἦσαν τάξις. See the remarks of Rüstow and Köchly upon the change made by Alexander in his military organization about this period, as soon as he found that there was no farther chance of a large collected Persian force, able to meet him in the field (Geschichte des Griech. Kriegswesens, p. 252 _seq._). The change which they point out was real,—but I think they exaggerate it in degree.