Domnonée is the modern French form of Domnonia or Dumnonia (Latin for "Devon"; Breton: Domnonea), an historic kingdom in northern Armorica (Brittany) founded by British immigrants from Dumnonia (Sub-Roman Devon) fleeing the Saxon invasions of Britain in the early Middle Ages. Headed by the same ruling family, it was variously separate or united with its motherland and its Latin name was used for both indiscriminately. The mainland territory of Domnonée included Trégor, Dol-de-Bretagne through to Goélo, and Penthièvre.
At the time of the Roman conquest of Gaul, the rough area of later Domnonée was held by the pagan Curiosolite Gauls. Domnonée is said[who?] to have been founded in the 4th century by Christian Briton immigrants; it greatly expanded in the wake of subsequent waves of refugees from the Saxon invasions of Britain. Domnonée retained close political links between the Celtic territories in Britain (Wales, Cornwall, Devon), and the newly created Brittany. Many kings, princes, clerics and other leaders came over from Britain. The sea was a unifying rather than divisive factor. In the traditions relating to the settlement of Brittany by the Bretons there are several kingdoms of this kind. A number of legends and lives of Breton saints contain references to the close political ties between religious communities in Wales and Brittany. The close proximity resulted in possessions on both sides of the Channel by some religious orders. For example, the Abbey of Notre-Dame de Beauport, before Henry VIII, had parishes on the coast of Goélo and in Devon.
It has been suggested that the British and Breton branches were unified for a period. Conomor, who was killed fighting Clotaire I, king of the Franks, is referred to in stories from both Britain and Brittany. He would have been a British military leader who was guarding the Channel from attacks by pirates, perhaps in alliance with Childebert I, son of Clovis.
Situated to the north east of Brittany, the earliest princes are mentioned in several Lives of the Saints. The three Armorican principalities were all subservient to the King of Brittany. Until the reign of Jonas, the rulers of Domnonia were titled princes. After that, they supply the Kings of the Bretons, and Domnonia itself was elevated as a result.