Which British king resisted Julius Caesar's invasions in 55 and 54 BC?

Cassivellaunus was the British leader who resisted Julius Caesar’s invasions of Britain in 55 and 54 BC. Caesar’s first expedition reached Britain in 55 BC but achieved little beyond a landing in Kent; the larger second invasion came the following year.

Cassivellaunus, associated with the Catuvellauni, was chosen to command a coalition of British tribes. He avoided a decisive pitched battle and used chariots, local knowledge, raids, and attacks on Roman foraging parties to slow Caesar’s advance. He also fortified the Thames crossing with sharpened stakes.

Caesar eventually reached Cassivellaunus’s territory after several tribes, including the Trinovantes, switched sides and revealed the location of his stronghold. Pressure increased when Roman forces defeated an attack on their coastal camp. Cassivellaunus then surrendered, agreed to pay tribute, and promised not to attack Mandubracius, whom Caesar restored as king of the Trinovantes.

A common mix-up is to treat Caesar’s expeditions as a conquest. They were not: Rome gained no permanent territory, and the lasting conquest of Britain began under Emperor Claudius in AD 43.