I agree with pezhetairoi on this. Ariovistus and his troops according to JC were brought over as mercenaries. They defeated the Aedui and then turned on the Sequani. Also during this time some of the Belgic and Celtic tribes enlisted Germani to help them against the Romans. The Gauls of the Po Valley also enlisted the Gaesatae mercenaries against the Romans in the 220's.