Cassivellaunus Cassivellaunus was a historical British chieftain who led the defence against Julius Caesar ' s second expedition to Britain in 54 BC . The first British person whose name is recorded , Cassivellaunus led 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 , " * Kađđiwellaunos " , comes from Proto - Celtic * kađđi - " passion , love , hate " ( alternately , " long hair " , or " bronze " ) + * welnamon - " leader , sovereign " . History . Cassivellaunus is the first British individual known to history . He 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 . Legend . " Historia Regum Britanniae " . Cassivellaunus appears in Geoffrey of Monmouth ' s 12th century work " Historia Regum Britanniae " ( " History of the Kings of Britain " ) , usually spelled Cassibelanus or Cassibelaunus . The younger son of the former king Heli , he becomes king of Britain upon the death of his elder brother Lud , whose own sons Androgeus and Tenvantius are not yet of age . In recompense , Androgeus is made Duke of Kent and Trinovantum ( London ) , and Tenvantius is made Duke of Cornwall . After his conquest of Gaul , Julius Caesar sets his sights on Britain , and sends a letter to Cassibelanus demanding tribute . Cassibelanus refuses , citing the Britons ' and Romans ' common Trojan descent ( see Brutus of Britain ) , and Caesar invades at the Thames Estuary . During the fighting , Cassibelanus ' s brother Nennius encounters Caesar and sustains a severe head wound . Caesar ' s sword gets stuck in Nennius ' s shield , and when the two are separated in the mêlée , Nennius throws away his own sword and attacks the Romans with Caesar ' s , killing many , including the tribune Labienus . The Britons hold firm , and that night Caesar flees back to Gaul . Cassibelanus ' s celebrations are muted by Nennius ' s death from his head wound . He is buried with the sword he took from Caesar , which is named " Crocea Mors " ( Yellow Death ) . Two years later , Caesar invades again with a larger force . Cassibelanus , forewarned , had planted stakes beneath the waterline of the Thames which gut Caesar ' s ships , drowning thousands of men . The Romans are once again quickly put to flight . The leaders of the Britons gather in Trinovantum to thank the gods for their victory with many animal sacrifices and celebrate with sporting events . During a wrestling bout , Cassibelanus ' s nephew Hirelglas is killed by Androgeus ' s nephew Cuelinus . Cassibelanus demands that Androgeus turn his nephew over to him for trial , but Androgeus refuses , insisting he should be tried in his own court in Trinovantum . Cassibelanus threatens war , and Androgeus appeals to Caesar for help . Caesar invades a third time , landing at Richborough . As Cassibelaunus ' s army meets Caesar ' s , Androgeus attacks Cassibelaunus from the rear with five thousand men . His line broken , Cassibelanus retreats to a nearby hilltop . After two days siege , Androgeus appeals to Caesar to offer terms . Cassibelanus agrees to pay tribute of three thousand pounds of silver , and he and Caesar become friends . Six years later , Cassibelanus dies and is buried in York . Androgeus has gone to Rome with Caesar , so Tenvantius succeeds as king of Britain . Welsh literature . Cassivellaunus appears as Caswallawn , son of Beli Mawr , in the Welsh Triads , the " Mabinogion " , and the Welsh versions of Geoffrey ' s " Historia Regum Britanniae " known as the " Brut y Brenhinedd " . In the Second Branch of the Mabinogi , he appears as a usurper , who seizes the throne of Britain while the rightful king , Bran the Blessed , is at war in Ireland . Using a magic cloak which renders him invisible , he kills the seven stewards Bran has left in charge , while the eighth , Bran ' s son Caradog , dies of bewilderment at the sight of a disembodied sword killing his men . He then appears in the Third Branch , in which Bran ' s followers offer their submission to him to avoid fighting . He is also mentioned in the tale " Lludd and Llefelys " , which features his two brothers Lludd Llaw Eraint ( Geoffrey ' s Lud ) and Llefelys . Caswallawn is referenced frequently in the Welsh Triads . Triad 51 describes his conflict with " Afarwy " ( Mandubracius / Androgeus ) as described in Geoffrey of Monmouth , while Triad 95 references the story of Caradawg son of Bran ' s death as told in the " Mabinogion " . However , other triads ( 35 , 36 , 38 , 59 , 67 , and 71 ) refer to a tradition about Caswallawn not drawn from either Roman nor existing medieval sources . Triad 38 names his horse as Meinlas ( " Slender Gray " ) and calls him one of the Three Bestowed Horses of the Island of Britain ; this is echoed in Triad 59 , in which the decision to allow the Romans to land in Britain in exchange for Meinlas is called one of the Three Unfortunate Counsels of the Island of Britain . Triad 35 indicates that Caswallawn left Britain with 21 , 000 men in pursuit of Caesar and never returned . Triads 67 and 71 portray Caswallawn as a great lover , who competed with Caesar over the beautiful Fflur . He is named as one of the Three Golden Shoemakers of the Island of Britain in relation to his trip to Rome seeking his love ; context suggests he disguised himself as a shoemaker . A later collection of triads compiled by the 18th - century Welsh antiquarian Iolo Morganwg gives an expanded version of this tradition , including the details that Caswallawn had abducted Fflur from Caesar in Gaul , killing 6 , 000 Romans , and that Caesar invaded Britain in response . As with the rest of Morganwg ' s Triads , however , the provenance of these references is suspect . However , the 12th - century poet Cynddelw Brydydd Mawr knew of some version of the Fflur story , writing that Caesar ' s love for her was costly . Welsh scholar Rachel Bromwich suggests the fragmentary allusions to Caswallawn in the Triads relate to a narrative of the character that has been lost . This may have been in the form of a romance detailing the king ' s adventures , but would have been largely uninfluenced by the classical accounts .