What is "erispoe"

Erispoe (; , , or ; 2 or 12 November 857) was Duke of Brittany from 851. After the death of his father Nominoe, he led a successful military campaign against the Franks, culminating in his victory at the Battle of Jengland. He is subsequently referred to as "King of Brittany".

Erispoe's recorded titles include provinciæ Brittaniæ princeps ("prince of the province of Brittany"), dux Brittonum ("duke of the Bretons"), and rex tyrannicus Brittonum ("usurping king of the Bretons"). However, if Erispoe was usurping regality in Brittany at that time (857), it is not attested in other sources. It may imply continued Frankish resentment of the title. He is called rex Brittonum ("king of the Bretons") by Regino of Prüm (d. 915).