During the Roman invasion of 43 AD the Brigantes were arguably the most powerful Celtic tribe in Britain, dominating the north of the country. In the beginning, led by their queen Cartimandua and her husband Venutius, they were on friendly terms with the Romans, acting as a "client-kingdom", a nominally independent ally beholden to Roman power. In about 51 AD the British resistance leader Caratacus was defeated by Publius Ostorius Scapula in Wales, and fled north to the Brigantes. Cartimandua proved her loyalty by handing Caratacus over to the Romans.
This was followed by a split with Venutius, who became the most prominent figure in the resistance to Rome. Cartimandua had apparently tired of him and married his armour-bearer, Vellocatus, who she elevated to the kingship in Venutius's place. Initially Venutius only sought to overthrow his ex-wife, only later turning his attention to her Roman protectors. The Romans defended their client queen, and Venutius's revolt was defeated by Caesius Nasica during the governorship of Aulus Didius Gallus (52 to 57 AD).
Taking advantage of Roman instability during the year of four emperors, Venutius revolted again in 69 AD. Cartimandua appealed for troops from the Romans, who were only able to send auxiliaries. Cartimandua was evacuated and Venutius took the kingdom.
It is not known whether the Brigantes in Europe settle in Britain, or vice versa.
She was ruler over the Brigantes, having the influence that belongs to high birth, and she had later strengthened her power when she was credited with having captured King Caratacus by treachery and so furnished an adornment for the triumph of Claudius Caesar.
Her husband was favoured by the sentiments of all the citizens; the adulterer was supported by the queen's passion for him and by her savage spirit.