Cassivellaunus was a historical British chieftain who led the defence against Julius Caesar’s second expedition to Britain in 54 BC. He headed an alliance of tribes against Roman forces, but eventually surrendered after his location was revealed to Caesar by defeated Britons.
Cassivellaunus made an impact on the British consciousness. He appears in British legend as Cassibelanus, one of Geoffrey of Monmouth’s kings of Britain, and in the Mabinogion, the Brut y Brenhinedd and the Welsh Triads as Caswallawn, son of Beli Mawr.
His name in Brythonic, Cassiuellaunos, comes from Proto-Celtic cassi- “passion, love, hate” (alternately, “long hair”, or “bronze”) uelna-mon- “leader, sovereign”.
Cassivellaunus appears in Julius Caesar’s Commentarii de Bello Gallico, having been given command of the combined British forces opposing Caesar’s second invasion of Britain. Caesar does not mention Cassivellaunus’s tribe, but his territory, north of the River Thames, corresponds with that inhabited by the tribe named the Catuvellauni at the time of the later invasion under Claudius.
Caesar tells us that Cassivellaunus had previously been at constant war with the British tribes, and had overthrown the king of the Trinovantes, the most powerful tribe in Britain at the time. The king’s son, Mandubracius, fled to Caesar in Gaul. Despite Cassivellaunus’s harrying tactics, designed to prevent Caesar’s army from foraging and plundering for food, Caesar advanced to the Thames. The only fordable point was defended and fortified with sharp stakes, but the Romans managed to cross it. Cassivellaunus dismissed most of his army and resorted to guerilla tactics, relying on his knowledge of the territory and the speed of his chariots.
Five British tribes, the Cenimagni, the Segontiaci, the Ancalites, the Bibroci and the Cassi, surrendered to Caesar and revealed the location of Cassivellaunus’s stronghold, thought to be at Wheathampstead, which Caesar proceeded to put under siege.
Cassivellaunus managed to get a message to the four kings of Kent, Cingetorix, Carvilius, Taximagulus and Segovax, to gather their forces and attack the Roman camp on the coast, but the Romans defended themselves successfully, capturing a chieftain called Lugotorix. On hearing of the defeat and the devastation of his territories, Cassivellaunus surrendered. The terms were mediated by Commius, Caesar’s Gallic ally. Hostages were given and a tribute agreed. Mandubracius was restored to the kingship of the Trinovantes, and Cassivellaunus undertook not to wage war against him. All this achieved, Caesar returned to Gaul where a poor harvest had caused unrest. The Roman legions did not return to Britain for another 97 years.
The Greek author Polyaenus relates an anecdote in his Stratagemata that Caesar overcame Cassivellaunus’s defence of a river crossing by means of an armoured elephant. This outlandish claim probably derives from a confusion with the Roman conquest of 43 AD, when Claudius is supposed to have brought elephants to Britain