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Rh the lower part of Palestine across the great Syrian Desert was then, as ever, 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; 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