Caratacus and his brother Togodumnus led the initial defence of the country against Aulus Plautius's legions, primarily using guerrilla tactics, but were defeated in two crucial battles on the rivers Medway (see Battle of Medway) and Thames. Togodumnus was killed and the Catuvellauni's territories conquered, but Caratacus survived and carried on the resistance further west.

Caratacus is found in Tacitus's Annals, leading the Silures and Ordovices in what is now Wales against Plautius's successor as governor, Publius Ostorius Scapula. A fort was erected in 49 AD near what is now Gloucester. Along with this fort and a network of others brought pressure to bear upon the Silures, which forced Caratacus to flee to the Ordovices. In 51, Scapula managed to defeat Caractacus in the Battle of Caer Caradock somewhere in Ordivician territory, capturing Caractacus's wife and daughter and receiving the surrender of his brothers. Caratacus himself escaped, and fled north to the lands of the Brigantes. The Brigantian queen, Cartimandua, however, was loyal to Rome, and she handed him over in chains.

Caractacus supposedly made the following speech taken from the 'Tacitus Annals':

"Had my moderation in prosperity been equal to my noble birth and fortune,
I should have entered this city as your friend rather than as your
captive; and you would not have disdained to recieve, under a treaty of
peace, a king descended from illustrious ancestors and ruling many
nations. My present lot is as glorious to you as it is degrading to
myself. I had men and horses, arms and wealth. What wonder if I parted
with them reluctantly? If you Romans choose to lord it over the world,
does it follow that the world is to accept slavery? Were I to have been
at once delivered up as a prisoner, neither my fall nor your triumph would
have become famous. My punishment would be followed by oblivion, whereas,
if you save my life, I shall be an everlasting memoirial of your clemency."