The Catuvellauni are classified as a Celtic tribe. They lived in Britain in the present-day county of Hertfordshire in southern England and are discussed as Celts or as Britons. With the Atrebates and Trinovantes, they were one of the three most powerful tribal kingdoms in Britain in the first centuries b. c.e. and c. e.
The Catuvellauni leader Cassivellaunus (perhaps of the Cassi) resisted the Romans under Julius Caesar in 54 b. c.e. After their defeat they established trade contacts and competed to control the imports of Roman goods.
In 10 c. e. the territories of the Catuvellauni and the Trinovantes were united by the Catuvellaunian king Cunobelin (Cymbeline). In 42 c. e. his sons, Caractacus (Caradoc) and Togodumnus, inherited his kingdom and moved against the pro-Roman Atrebates (One theory of the rationale for the Roman invasion of Britain in 43 c. e. was that the Atrebates appealed to Rome for help against the Catuvellauni.) Afterward Caractacus and allies in Wales among the Ordovices and Silures resisted Roman occupation. He eventually sought refuge among the Brigantes under Queen Cartimandua in 51 c. e., but she turned him over to the Romans.
Verulamium on the site of present-day St. Albans became a civitas capital during the Roman occupation lasting until 410 c. e. Londinium on the site of present-day London, another Catuvellauni town, eventually became the capital in Roman Britain. They were both attacked in the revolt led by Queen Boudicca (Boadicea) of the Iceni. A tribe known as Catuvellauni, probably related ancestrally, inhabited part of Gaul near the Senones and would thus be discussed as Gauls.