Caratacus is named by Dio Cassius as a son of the Catuvellaunian king Cunobelinus. Based on coin distribution Caratacus appears to have been the protegé of his uncle Epaticcus, who expanded Catuvellaunian power westwards into the territory of the Atrebates. After Epaticcus died ca. 35, the Atrebates, under Verica, regained some of their territory, but it appears Caratacus completed the conquest, as Dio tells us Verica was ousted, fled to Rome and appealed to the emperor Claudius for help. This was the excuse used by Claudius to launch his invasion of Britain in the Summer of 43.
Cunobelinus had died some time before the invasion. Caratacus and his brother Togodumnus led the initial defence of the country against Aulus Plautius's four legions thought to have been around 40,000 men, primarily using guerrilla tactics. They lost much of the south-east after being defeated in two crucial battles on the rivers Medway and Thames. Togodumnus was killed and the Catuvellauni's territories were conquered. Claudius was present in August when his legions marched into Camulodunum, the capital of the Catuvellauni , but Caratacus survived and carried on the resistance further west.
We next hear of Caratacus in Tacitus's Annals, leading the Silures and Ordovices of Roman Wales against Plautius' successor as governor, Publius Ostorius Scapula. Finally, in 51, Scapula managed to defeat Caratacus in a set-piece battle somewhere in Ordovician territory (see the Battle of Caer Caradoc), capturing Caratacus' wife and daughter and receiving the surrender of his brothers. Caratacus himself escaped, and fled north to the lands of the Brigantes (modern Yorkshire where the Brigantian queen, Cartimandua handed him over to the Romans in chains. (This was one of the factors that led to two Brigantian revolts against Cartimandua and her Roman allies, once later in the 50s and once in 69, led by Venutius, who had once been Cartimandua's husband). With the capture of Caratacus, much of southern Britain from the Humber to the Severn was pacified and garrisoned throughout the 50s .
[Caratacus] resorted to the ultimate hazard, adopting a place for battle so that entry, exit, everything would be unfavorable to us and for the better to his own men, with steep mountains all around, and, wherever a gentle access was possible, he strewed rocks in front in the manner of a rampart. And in front too there flowed a stream with an unsure ford, and companies of armed men had taken up position along the defenses.
Although the Severn is visible from British Camp, it is nowhere near it, so this battle must have taken place elsewhere. A number of locations have been suggested, including a site near Brampton Bryan.
After his capture, Caratacus was sent to Rome as a war prize, presumably to be killed after a triumphal parade. Although a captive, he was allowed to speak to the Roman senate. Tacitus records a version of his speech in which he says that his stubborn resistance made Rome's glory in defeating him all the greater:
If the degree of my nobility and fortune had been matched by moderation in success, I would have come to this City as a friend rather than a captive, nor would you have disdained to receive with a treaty of peace one sprung from brilliant ancestors and commanding a great many nations. But my present lot, disfiguring as it is for me, is magnificent for you. I had horses, men, arms, and wealth: what wonder if I was unwilling to lose them? If you wish to command everyone, does it really follow that everyone should accept your slavery? If I were now being handed over as one who had surrendered immediately, neither my fortune nor your glory would have achieved brilliance. It is also true that in my case any reprisal will be followed by oblivion. On the other hand, if you preserve me safe and sound, I shall be an eternal example of your clemency.
He made such an impression that he was pardoned and allowed to live in peace in Rome. After his liberation, according to Dio Cassius, Caratacus was so impressed by the city of Rome that he said "And can you, then, who have got such possessions and so many of them, covet our poor tents?
Caratacus' memory may 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", preserving the names of the three historical figures in correct relationship.
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 Kymbelinus, who continues to resist the Roman invasion after the death of his older brother Guiderius. In Welsh versions his name is Gweirydd, 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 agree that he was Bran's son, and name two sons, Cawrdaf and Eudaf.
Another tradition, which has remained popular among British Israelites and others, makes Caratacus already a Christian before he came to Rome, Christianity having been brought to Britain by either Joseph of Arimathea or St. Paul, and identifies a number of early Christians as his relatives.
One is Pomponia Graecina, wife of Aulus Plautius, the conqueror of Britain, who as Tacitus relates, was accused of following a "foreign superstition", generally considered to be Christianity. Tacitus describes her as the "wife of the Plautius who returned from Britain with an ovation", which led John Lingard (1771 – 1851) to conclude, in his History and Antiquities of the Anglo-Saxon Church, that she was British; however, this conclusion is a misinterpretation of what Tacitus wrote. An ovation was a military parade in honour of a victorious general, so the person who "returned from Britain with an ovation" is clearly Plautius, not Pomponia. This has not prevented the error being repeated and disseminated widely.
Another is Claudia Rufina, a historical British woman known to the poet Martial. Martial describes Claudia's marriage to a man named Pudens, almost certainly Aulus Pudens, an Umbrian centurion and friend of the poet who appears regularly in his Epigrams. It has been argued since the 17th century that this pair may be the same as the Claudia and Pudens mentioned as members of the Roman Christian community in 2 Timothy in the New Testament. Some go further, claiming that Claudia was Caratacus' daughter, and that the historical Pope Linus, who is described as the "brother of Claudia" in an early church document, was Caratacus' son. Pudens is identified with St. Pudens, and it is claimed that the basilica of Santa Pudenziana in Rome, and with which St. Pudens is associated, was once called the Palatium Britannicum and was the home of Caratacus and his family.
This theory was popularised in a 1961 book called The Drama of the Lost Disciples by George Jowett, but Jowett did not originate it. He cites renaissance historians such as Archbishop James Ussher, Caesar Baronius and John Hardyng, as well as classical writers like Caesar, Tacitus and Juvenal, although his classical cites at least are wildly inaccurate, many of his assertions are unsourced, and many of his identifications entirely speculative. He also regularly cites St. Paul in Britain, an 1870 book by R. W. Morgan, and advocates other tenets of British Israelism, in particular that the British are descended from the lost tribes of Israel.