Wikipedia
The Catuvellauni were a Celtic tribe or state of south-eastern Britain before the Roman conquest, attested by inscriptions into the 4th century.
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 that 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 the town of Verlamion (modern St Albans) and the surrounding areas of Hertfordshire, Bedfordshire and southern Cambridgeshire.
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.