The Breton ruler was sometimes elected, sometimes attained the position by conquest or intrigue, or by hereditary right.
Hereditary dukes were sometimes a female ruler, carrying the title duchesse of Brittany.
During the declining years of the Roman Empire, the earliest Breton rulers in Gaul were styled "kings" of the small realms of Cornouaille and Domnonée.
[2] The area was often called a Duchy, and its monarchs were considered independent Sovereign Dukes.
The succession was interrupted by the Viking occupation (913–937) Eleanor, Fair Maid of Brittany, eldest daughter of Geoffrey and Constance and full elder sister of Arthur, also unmarried, was prevented from succession by her imprisonment in England which lasted till her death in 1241, thus was merely a titular duchess from 1208 to 1214 when John, King of England ceased to support her claim.