If he did not find the Egyptians there, Perdiccas would install himself within one of the fortresses on that side, and thence conduct operations against them, and, at the same time, remain in connection with his fleet, on which he could fall back in case of need. To enable the crossing to be accomplished as easily as possible, Perdiccas ordered the cleaning out of an old and filled-in canal, that led up from the Nile. The work was evidently begun without much thought, for the fact had not been considered that, at the rising of the Nile, the canal would want a much deeper bed than the present stream required. The canal had only just been opened up, when the water rose with unusual force and rapidity; the dam was completely destroyed, and many workers lost their lives. During the disturbance, many officers and men left the camp and hurried to Ptolemy. This was the beginning of the Egyptian war. The desertion of so many important men made Perdiccas think seriously. He summoned the officers of the army, spoke to them with much condescension, gave presents to some, honoured others with promotion, and begged them, for the sake of their honour and for the cause of their kings, to fight their hardest against this rebel, and with the order to hold their men in-readiness, he left them. The army was only told in the evening, at the signal for starting, where they were to march. Perdiccas feared, on account of the desertion that was taking place in his army, that his march might be discovered by the enemy. They marched with great speed through the night, and camped at last on the side of the river. At daybreak, after the troops had rested, Perdiccas gave the order to cross. First came the elephants, then the light infantry, next the storming party with ladders, and lastly, the pick of the cavalry, who, if the enemy should burst out during the storming, could easily drive them back. Perdiccas hoped, if he could only get a firm footing on that side of the river, to annihilate the Egyptian army easily with his superior force. He was right in feeling that his Macedonian troops, when face to face with the enemy, would forget their antipathy to him, and think only of their military honour. When about half the army had crossed, and just as the elephants were moving towards the fortress, the enemy were seen hurrying thither with great speed; their trumpet-calls and war-cries even were heard. They reached the fort before the Macedonians, and withdrew into the shelter of its walls. Not discouraged by this, the infantry stormed the fort. Ladders were placed against the walls, the elephants driven forward, and palisades taken from their backs to attack the ramparts.