It is not known where this battle was fought, but Snowdonia was at the very heart of the territory of the Ordovices. If Caratacus was defeated there and not in the land of the Catuvellauni, it may be, in part, because of what happened a hundred years before.

His father Cunobelin (Cunobelinus) had been king of the Catuvellauni, the most powerful tribe in southern Britain, and the son of Tasciovanus, whose coins bear the name of Verulamium (St. Albans), then the tribal capital. And Tasciovanus probably was the son of Cassivellaunus, who had led the Britons against Caesar during his second invasion in 54 BC.

Caesar relates what happened. After several defeats, Cassivellaunus fought a guerrilla action, harassing the Romans until, eventually, the location of his stronghold (oppidium) was betrayed by the Trinovantes, whose own king had been killed by Cassivellaunus and who now allied themselves with Caesar. Cassivellaunus was defeated and was obliged to pay tribute and surrender hostages. He also was forced to give the Trinovantes their independence.

Caesar then returned to Gaul. But the Catuvellauni soon reasserted themselves and became the dominant tribe in southeastern Britain. The Trinovantes were able to maintain their independence, however, until the time of Cunobelin, who seized Camulodunum, their capital. Even though the two tribes now became essentially a single kingdom, the Trinovantes again were regarded as a separate tribe by the Romans when the Catuvellauni were defeated by Claudius in AD 43, and, by the time of the Boudican revolt in AD 60, it is the Trinovantes who are driven from their land by the Roman colonists.

From Encyclopedia Romana