Caesar then returned to the Stour crossing and found the Britons had massed their forces there. Cassivellaunus, a warlord from north of the Thames, had previously been at war with most of the British tribes. He had recently overthrown the king of the powerful Trinovantes and forced his son, Mandubracius, into exile. But now, facing invasion, the Britons had appointed Cassivellaunus to lead their combined forces. After several indecisive skirmishes, during which a Roman tribune, Quintus Laberius Durus, was killed, the Britons attacked a foraging party of three legions under Gaius Trebonius, but were repulsed and routed by the pursuing Roman cavalry.