A short-lived independent kingdom uniting Brittany's petty rulers under Erispoe after Frankish recognition in 851, building on Nominoe's earlier revolt (Battle of Ballon, 845) against Carolingian overlordship.
Weakened by dynastic assassination (Erispoe murdered by his cousin Salomon, 857) and repeated Viking raids from the 910s; the royal title lapsed after Alan I's death (907) and a Norse takeover, and Brittany continued as a duchy under nominal Frankish/French suzerainty once Alan II restored native rule in 939.
Standard dedicated academic history of early medieval Brittany, spanning the period of this kingdom.