After a battle with the Nervii, in which Cæsar defeated them disastrously, largely because of his resourcefulness in emergency and their lack of it, he advanced against a great barbarian stronghold that looked down on steep rocks on three sides, and was protected by a thick, high double wall on the fourth side. Cæsar made a fortified rampart around the town, pushed his mantlets (large shields on wheels protected on the sides and top) close up to the wall, and built a tower. The barbarians laughed at this tower; seeing it so far away that, they thought, no darts thrown from it could reach them. But when they saw the tower actually moving toward them they were struck with terror and began at once to sue for peace. During the following winter the Veneti, a large tribe on the northwestern coast, the most skilful seamen and navigators of Gaul, stirred up a revolt that quickly and widely spread. The situation at once became serious for Cæsar, for the reason that the Veneti could not be subdued, except on the sea; and neither the Roman sailors nor the Roman vessels were as good as were those of the Veneti. Nevertheless, Cæsar ordered war-vessels to be built on the Loire River, and seamen and rowers to be drafted from the Roman Province. When the improvised fleet of the Romans and the thoroughly prepared fleet of the Veneti came together, the latter was superior even in numbers. Furthermore, the Romans were at a great disadvantage in the matter of throwing projectiles, from the fact that the Veneti's decks were higher than theirs. But Cæsar had prepared a scheme that gave him victory. In accordance with it, the Roman galleys rowed smartly against the Veneti ships, and Roman sailors raised long poles on which were sharp hooks which they put over the halliards that held up the sails. Then each Roman galley rowed rapidly away, the halliards were cut, and down came the sails. The Veneti ships became helpless at once and were immediately boarded; with the result that, of all the number, only a few made their escape. Somewhat later, Cæsar decided to cross the Rhine into the country of the Sueves, and to impress them with the power of Rome by building a bridge and marching his army across. This bridge and the quickness and thoroughness with which it was built are still models for engineers; for in ten days after he had decided to build it, at which time the material was still standing in the forest, a bridge 40 feet wide had been constructed. Across this Cæsar at once marched his legions. The effect on the barbarous Germans can be imagined. It made them realize that the Romans were a race superior to themselves in ways that they could not measure or even understand; and it impressed them with that fear which is the most depressing of all fears, the fear of the unknown.