He had seen walls won and lost before.

To follow up such a venture with a strong detachment must result in one of two things, either the detachment in its turn must be supported by the entire army, or it must eventually retreat.

If it retreated, the loss of prestige would be serious, and might encourage the enemy to attack the camp, for it was only his prestige which prevented them.

If supported by the entire army, then the fate of the whole expedition depended upon that single day.
The enemy had the advantage of the wall, of the narrow streets and enclosures within, of the houses, each of which would become a fortress, and thus in the winding streets a repulse might easily happen.

To risk such an event would be folly in the last degree, before the town had been dispirited and discouraged by the continuance of the siege, the failure of their provisions, or the fall of their chief leaders in the daily combats that took place.
The army had no discipline whatever, beyond that of the attachment of the retainer to his lord, and the dread of punishment on the part of the slave.