The Duchy of Brittany (Breton: Dugelezh Breizh, French: Duché de Bretagne) was a medieval feudal state that existed between approximately 939[a] and 1547.[b] Its territory covered the northwestern peninsula of Europe, bordered by the Atlantic Ocean on the west and the English Channel to the north, and less definitively by the Loire River to the south and Normandy and other French provinces to the east.
More information on the Wikipedia page [1].