The islanders, meanwhile, had not been idle: messengers had been despatched in every direction, calling on the various nations to take arms; the Druids preached war to the death; and a sufficient force was soon assembled to attack the Romans in their camp. Discipline, however, again prevailed against the courage of the barbarians, as Tacitus contemptuously calls them; although he admits at the same time their bravery, and adds that it was a fortunate thing for Cæsar that the country was so divided into petty states that the jealousies of their respective rulers prevented the unity of action which alone could ensure success. Had the Britons been united, they might have bid defiance to the legions of Rome. Once more the islanders demanded peace, which Cæsar granted them; in fact, he was scarcely in a position to do otherwise, for he already meditated a retreat. He embarked the army suddenly in the night, and retired to Gaul, taking the hostages he had received with him. Although the senate of Rome ordered a thanksgiving of twenty days for the triumph of the Roman arms, the first expedition against the island cannot be regarded as other than a failure. For the second invasion, which took place in the following year, preparations were made commensurate with the importance of the task proposed. Cæsar having assembled 800 vessels, on board of which were five legions, and 2,000 horsemen of the noblest families in Gaul, set sail, and landed without opposition at Ryde. This time there was no enemy to oppose him; for the Britons, terrified at the appearance of this immense armament, had retreated to their natural fastnesses, the forests. Leaving ten cohorts and 300 horsemen to guard the camp and fleet, under the orders of Quintus Atrius, Cæsar set forward in search of the enemy, whom he discovered, after a march of twelve miles, on the banks of a river, where they had drawn up their chariots and horsemen. Profiting by their elevated position, they accepted, or rather engaged, the combat, and when repulsed withdrew into an admirably fortified camp, which was not taken without much difficulty. The Britons, as usual after a defeat, retreated once more to their woods, where it was impossible for the legions of Rome to follow, or the cavalry to act against them.