The Dumnonii is the Latin name for a Celtic tribe which emerged in the wake of the Roman withdrawal from
England during the 4th century A.D. Their territory spanned
Devon and
Cornwall with further holdings in Somerset
? and Dorset
?. They were possibly the most powerful of all the British Celtic tribes. It is also possible that the Dumnonii held some Breton land at some point. The name of Dumnonia in Celtic is Dunein.
Originally their capital would have been at Isca, (Exeter), although archaeological evidence indicates that Celtic occupation ended during the 5th century A.D., no doubt as a result of the expansion of the [West Saxons]?.
Dumnonia was effectively a collection of sub-kingdoms.