We know from Cassius Dio that he was a son of the notable British king Cunobelinus of the tribe known as the Catuvellauni. A series of coins inscribed CARA appear to indicate that for a brief period before the Roman conquest of AD 43 he ruled the region around Calleva Atrebatum (Silchester), which his uncle Epaticcus had seized from Verica of the Atrebates the previous decade. Dio tells us that "Bericus" (almost certainly Verica) was ousted and appealed to the Roman emperor Claudius for aid, prompting the conquest of the island.
Cunobelinus was dead by the time the invasion started. Caratacus and his brother Togodumnus led the initial resistance, but the Roman commander Aulus Plautius forced them to retreat beyond first the River Medway, then, after a difficult battle, the Thames. Shortly afterwards Togodumnus died. Plautius halted at the Thames and sent for Claudius, who arrived with reinforcements, artillery and elephants and led the march to Cunobelinus's capital, Camulodunum (Colchester). Dio says that Claudius's assistance was needed to overcome British resistance, but Suetonius says that Claudius "without any battle or bloodshed received the submission of a part of the island", and Claudius's own triumphal arch says "he received the surrender of eleven kings of the Britons defeated without any loss", so it is likely the Britons were already defeated by the time he arrived.
The next we hear of Caratacus he is leading the Silures of modern south Wales in a nine year war against the advancing Romans. Despite his numerical disadvantage, he used his knowledge of the terrain in a series of successful engagements. In 51 the governor Publius Ostorius Scapula marched against him. Caratacus moved his troops north, into the territory of the Ordovices, chose a battlefield on a hill behind a river, and built a stone rampart as further defence. He exhorted his men, appealing to their ancestors who had driven out Julius Caesar a century before, and telling them that the battle "would be the beginning of the recovery of their freedom, or of everlasting bondage". However, using the testudo formation, the Romans tore down the stone defences and stormed his position. Caratacus's wife, daughter and brothers were captured.
Caratacus himself fled north, and appealed to Cartimandua, queen of the Brigantes, for sanctuary, but Cartimandua handed him over to the Romans in chains, and he was taken to Rome to appear in Claudius's triumph. He made a speech appealing to his own nobility and Claudius's clemency, and saying "If you Romans choose to lord it over the world, does it follow that the world is to accept slavery?", which so impressed the emperor that he and his family were pardoned. After his liberation, he is said to have looked on the splendour of the city of Rome and said, "can you, then, who have got such possessions and so many of them, covet our poor tents?"
Caratacus's memory appears to have been preserved in medieval British tradition. A genealogy in the Welsh Harleian MS 3859 (ca. 1100) includes the generations "Caratauc map Cinbelin map Teuhant", corresponding, via established processes of language change, to "Caratacus, son of Cunobelinus, son of Tasciovanus", thus preserving the names of the three historical figures in correct relationship, although out of historical context.
Caratacus does not appear in Geoffrey of Monmouth's History of the Kings of Britain (1136), although he appears to correspond to Arviragus, the younger son of Kimbelinus, who continues to resist the Roman invasion after the death of his older brother Guiderius. In Welsh versions his name is Gweyrydd, son of Cynfelyn, and his brother is called Gwydyr. The name Arviragus is taken from a poem by Juvenal.
Caradog, son of Bran, who appears in medieval Welsh literature, has also been identified with Caratacus, although nothing in the medieval legend corresponds except his name. He appears in the Mabinogion as a son of Bran the Blessed, who is left in charge of Britain while his father makes war in Ireland, but is overthrown by Caswallawn (the historical Cassivellaunus, who lived a century earlier than Caratacus). The Welsh Triads name two sons, Cawrdaf and Eudaf. Caradog only began to be identified with Caratacus after the rediscovery of the works of Tacitus, and new material appeared based on this identification. An 18th century tradition, popularised by the Welsh antiquarian and forger Iolo Morganwg, credits Caradog, on his return from imprisonment in Rome, with the introduction of Christianity to Britain.
- Cassius Dio, Roman History 60:20
- Philip de Jersey, Celtic Coinage in Britain, Shire Archaeology, 1996, pp. 30-31
- Cassius Dio, Roman History 60:19
- Cassius Dio, Roman History 60:20-22
- Suetonius, Claudius 17
- Arch of Claudius
- Tacitus, Annals 12:33-35
- Tacitus, Annals 12:36-37
- Cassius Dio, Roman History 60:33.3c
- Harleian Genealogies 16; "The Heirs of Caratacus" - Caratacus and his relatives in medieval Welsh genealogies
- Geoffrey of Monmouth, Historia Regum Britanniae 4:12-16
- Peter Roberts (trans), The Chronicle of the Kings of Britain, 1811 (Llanerch Press facsimile reprint, 2000), pp. 83-89
- Juvenal, Satires 4.126-127
- The Mabinogion: "Branwen, daughter of Llyr"
- Rachel Bromwich, Trioedd Ynys Prydein, University of Wales Press, 1963
- Iolo Morganwg, Triads of Britain 17, 22, 23, 24, 34, 35, 41, 55, 79, 85, 91