Cassivellaunus was a British chieftain who led the resistance against the Roman invasion during the late 1st century BCE. He is best known for his role in the conflict with the Roman general Julius Caesar during the latter's expeditions to Britain in 55 and 54 BCE. Cassivellaunus was the leader of a coalition of tribes in southeastern Britain, and he utilized guerrilla tactics to challenge the Roman forces. Despite his efforts, Cassivellaunus ultimately surrendered to Caesar after a series of battles. Following his defeat, he was granted a peace treaty, which allowed him to retain some power in his territory. His resistance is often noted as a significant moment in the early history of Roman Britain.