These arrangements were duly carried out. Since it was too late for Pompey and Crassus to be candidates at the regular elections in 56 B. C., they forcibly prevented any elections being held that year. The following January, after forcing the other candidates to withdraw, they secured their election. Thereupon a law of the tribune Gaius Trebonius made effective the assignment of provinces agreed upon at Luca. Once more it was made plain that the coalition actually ruled the empire. Cicero, who was indebted to Pompey for his recall, was forced to support the triumvirate, and the Optimates found their boldest leader in Cato, who had returned to Rome early in 56 B. C. *Caesar’s crossing of the Rhine and invasion of Britain: 55–54 B. C.* During the winter following the subjugation of the Veneti, two Germanic tribes, the Usipetes and the Tencteri, crossed the lower Rhine into Gaul. In the next summer, 55 B. C., Caesar attacked and annihilated their forces, only a few escaping across the river. As a warning against future invasion, Caesar bridged the Rhine and made a demonstration upon the right bank, destroying his bridge when he withdrew. Towards the close of the summer he crossed the Straits of Dover to Britain, to punish the Britons for aiding his enemies in Gaul. But owing to the lateness of the season and the smallness of his force he returned to Gaul after a brief reconnaissance. In the following year, after gathering a larger fleet, he again landed on the island with a force of almost 30,000 men. This time he forced his way across the Thames and received the submission of Cassivellaunus, the chief who led the British tribes against the invaders. After taking hostages, and receiving promises of tribute, Caesar returned to Gaul. Britain was in no sense subdued, but the island had felt the power of Rome, and, besides enlarging the geographical knowledge of the time, Caesar had brought back numbers of captives. In Rome the exploit produced great excitement and enthusiasm. *Revolts in Gaul: 54–53 B. C.* Although the Gauls had submitted to Caesar, they were not yet reconciled to Roman rule, which put an end to their inter-tribal wars and to the feuds among the nobility. Consequently, many of the tribes were restive and not inclined to surrender all hopes of freedom without another struggle. In the course of the winter 54–53 B. C. the Nervii, Treveri and Eburones in Belgian Gaul attacked the Roman detachments stationed in their territories. One of these was cut to pieces but the rest held their ground until relieved by Caesar, who stamped out the rebellion.