The first attacks[209] were directed against the tower built in the middle of the Nile; vessels, in which were placed towers, ladders, and drawbridges, approached the walls. The soldiers who manned them, braving the arrows and murderous machines of the Mussulmans, made several assaults; but prodigies of strength, courage, and skill were useless. The most intrepid of the Crusaders, victims of their own rash bravery and devotedness, perished, swallowed up by the waves, without being able to be succoured or avenged by their companions. In all the attacks, nothing could equal the impetuous valour of the Western warriors; but this valour was not seconded by either the prudence of the commanders or the discipline of the soldiers; each nation had its leader, its machines of war, its days for fighting; no order governed either attack or retreat; the soldiers on board the vessels wished to manœuvre them, the sailors would fight. The frequent checks they experienced, at length, however, taught them prudence: the lightest of their vessels ascended the Nile, and returning to cast anchor above the tower built in the middle of the river, attacked and broke asunder the bridge of boats which united the tower with the city. Industry likewise lent its assistance to the bravery of the Crusaders; machines of war were invented, of which no models had previously existed. An enormous wooden castle, built upon two vessels,[210] joined together by beams and joists, was admired as a miraculous invention, and considered as a certain pledge of victory. Upon this floating castle was a drawbridge, which could be lowered upon the tower of the Saracens, and galleries destined to receive the soldiers who were to attack the walls. A poor priest of the church of Cologne,[211] who had preached the crusade on the banks of the Rhine, and followed the Christian army into Egypt, was charged with the superintendence of the erection of this formidable edifice. As the popes in their letters always advised the Crusaders to take with them to the East men skilled in the mechanical arts,[212] the Christian army was in no want of workmen to perform the most difficult labours; the liberality of the leaders and soldiers supplied all the necessary expenses.