The Catuvellauni were a tribe or state of south-eastern Britain before the Roman conquest.
The fortunes of the Catuvellauni and their kings before the conquest can be traced through numismatic evidence and scattered references in classical histories. They are mentioned by Dio Cassius, who implies they led the resistance against the conquest in AD 43. They appear as one of the civitates of Roman Britain in Ptolemy's Geography in the 2nd century, occupying modern Hertfordshire, Bedfordshire and southern Cambridgeshire and based around the town of Verlamion (modern St Albans).
Their territory was bordered to the north by the Iceni and Corieltauvi, to the east by the Trinovantes, to the west by the Dobunni and Atrebates, and to the south by the Regnenses and Cantiaci.
The Catuvellauni are etymologically unrelated to the Catalauni of Belgic Gaul. The name is derived from the Ancient British catu-uellauni meaning "battle-chieftains" or "battle-leaders". This ultimately derives from the Proto-Celtic *katu-, "battle", and *wel-nā-, "to lead".
Read more about Catuvellauni: Before The Roman Conquest, Under Roman Rule, List of Leaders of The Catuvellauni