One day, while the siege tower was being defended against those who were in charge of the town, the watch was being kept by Vasco Peres de Sampaio. While he was eating his evening meal in the siege camp, which lay some distance away from the tower, and heedless as to whether the townsmen would dare to attack it, there emerged from the town a detachment of soldiers, many of them carrying burning brands, each man as best he could, and despite those on watch, before help could reach them from the encampment, which was quite distant, they set fire to the tower, completely destroying it. From then on, the townsfolk had free access to all the water they wanted.

The king was extremely angry at this and made bitter complaints against Vasco Peres for the way in which it had come about. He realised that, even if he gave orders for another siege tower to be constructed, it would be difficult to guard it against damage, not only because of what had happened, but also because of the two [town’s] towers which were very near to that spot, even though they had started to batter them down. He decided, however, to construct another siege tower, closer to the encampment and near to one of the town's gates, where there stood a fine tower which was not so close that much damage could be inflicted from it. The siege tower was so powerfully held together with beams, reeds and lengths of rawhide that, though on one night the defenders inside the town had an engine from which they had hurled thirty rocks, of which twenty-seven had struck it, not one of them caused it any damage.

From this siege tower, which was higher than the town walls, they never stopped shooting from their crossbows and hurling stones at those who wanted to walk along them, with the result that nobody dared to be on it for fear of the injury they could receive from the tower. Likewise, frequent shooting from the [other] siege engines took place day and night, and they brought down many houses in the castle and the town, killing the soldiers and wreaking immense havoc.