_Fourth Campaign_, B.C. 55.--In the following year Caesar determined to attack the Germans. The Gauls had suffered too much in the last three campaigns to make any farther attempt against the Romans at present; but Caesar's ambition would not allow him to be idle. Fresh wars must be undertaken to employ his troops in active service. Two German tribes, the Usipetes and the Tenchtheri, had been driven out of their own country by the Suevi, and had crossed the Rhine with the intention of settling in Gaul. This, however, Caesar was resolved to prevent, and accordingly prepared to attack them. The Germans opened negotiations with him, but, while these were going on, a body of their cavalry defeated Caesar's Gallic horse. On the next day all the German chiefs came into Caesar's camp to apologize for what they had done; but Caesar detained them, and straightway led his troops to attack the enemy. Deprived of their leaders and taken by surprise, the Germans, after a feeble resistance, took to flight, and were almost all destroyed by the Roman cavalry. After this victory Caesar resolved to cross the Rhine, in order to strike terror into the Germans. In ten days he built a bridge of boats across the river, probably in the neighborhood of Cologne; and after spending eighteen days on the eastern side of the Rhine, and ravaging the country of the Sigambri, he returned to Gaul and broke down the bridge. Although the greater part of the summer was now gone, Caesar resolved to invade Britain. His object in undertaking this expedition at such a late period of the year was more to obtain some knowledge of the island from personal observation than with any view to permanent conquest at present. He accordingly took with him only two legions, with which he sailed from the port Itius (probably Witsand, between Calais and Boulogne), and effected a landing somewhere near the South Foreland, after a severe struggle with the natives. Several of the British tribes hereupon sent offers of submission to Caesar; but, in consequence of the loss of a great part of the Roman fleet a few days afterward, they took up arms again. Being, however, defeated, they again sent offers of submission to Caesar, who simply demanded double the number of hostages he had originally required, as he was anxious to return to Gaul before the autumnal equinox. The news of these victories over the Germans and far-distant Britons was received at Rome with the greatest enthusiasm. The Senate voted a public thanksgiving of twenty days, notwithstanding the opposition of Cato, who declared that Caesar ought to be delivered up to the Usipetes and Tenchtheri, to atone for his treachery in seizing the sacred persons of embassadors.