On learning that Darius was with a large army on the left of the Tigris, Alexander hurried forward and crossed that river without opposition. He was at first unable to procure any certain intelligence of the precise position of the enemy, and after giving his army a short interval of rest, he marched for four days down the left bank of the river. A moralist may pause upon the fact, that Alexander must in this march have passed within a few miles of the remains of Nineveh, the great, city of the primaeval conquerors of the human race. Neither the Macedonian king nor any of his followers knew what those vast mounds had once been. They had already become nameless masses of grass-grown ruins; and it is only within the last few years that the intellectual energy of one of our own countrymen has rescued Nineveh from its long centuries of oblivion. [See Layard's "Nineveh," and also Vaux's "Nineveh and Persepolis," p. 16.] On the fourth day of Alexander's southward march, his advanced guard reported that a body of the enemy's cavalry was in sight. He instantly formed his army in order for battle, and directing them to advance steadily, he rode forward at the head of some squadrons of cavalry, and charged the Persian horse whom he found before him. This was a mere reconnoitring party, and they broke and fled immediately; but the Macedonians made some prisoners, and from them Alexander found that Darius was posted only a few miles off and learned the strength of the army that he had with him. On receiving this news, Alexander halted, and gave his men repose for four days, so that they should go into action fresh and vigorous. He also fortified his camp, and deposited in it all his military stores, and all his sick and disabled soldiers; intending to advance upon the enemy with the serviceable part of his army perfectly unencumbered. After this halt, he moved forward, while it was yet dark, with the intention of reaching the enemy, and attacking them at break of day. About half-way between the camps there were some undulations of the ground, which concealed the two armies from each other's view. But, on Alexander arriving at their summit, he saw by the early light the Persian host arrayed before him; and he probably also observed traces of some engineering operation having been carried on along part of the ground in front of them. Not knowing that these marks had been caused by the Persians having levelled the ground for the free use of their war-chariots, Alexander suspected that hidden pitfalls had been prepared with a view of disordering the approach of his cavalry. He summoned a council of war forthwith, some of the officers were for attacking instantly at all hazards, but the more prudent opinion of Parmenio prevailed, and it was determined not to advance farther till the battle-ground had been carefully surveyed.