A need for prestige more than tactical concerns likely determined Caesar's campaigns in 55 BC. Pompey and Crassus were the consuls that year. While they were Caesar's political allies, and Crassus's son had fought under him the year before, they were also his rivals. Since the consuls could easily sway and buy public opinion, Caesar needed to stay in the public eye. His solution was to cross two water bodies no Roman army had attempted before: the Rhine and the English Channel. Crossing the Rhine was a consequence of Germanic/Celtic unrest. The Suebi had recently forced the Celtic Usipetes and Tencteri from their lands and had crossed the Rhine in search of a new home. Caesar, however, had denied their earlier request to settle in Gaul, and the issue turned to war. The Celtic tribes sent out a cavalry force of 800 against a Roman auxiliary force of 5,000 made up of Gauls, and won a surprising victory. Caesar responded by attacking the Celtic camp, and slaughtering the men, women, and children. Caesar claims he killed 430,000 people in the camp. Modern historians dispute this number (see historiography below), but it is apparent that Caesar killed a great many Celts. So cruel were his actions, his enemies in the Senate wished to prosecute him for war crimes once his tenure as governor was up and he was no longer immune from prosecution. After the massacre, Caesar led the first Roman army across the Rhine in a lightning campaign that lasted just 18 days.