Cyfeilliog

Cyfeilliog (Welsh pronunciation: [kəˈvɛiɬjɔɡ]) or Cyfeiliog^[2] (Welsh: [kəˈvɛiljɔɡ], in Old Welsh Cemelliauc; probably died 927), was a bishop in south-east Wales. The location and extent of his diocese is uncertain, but lands granted to him are mainly close to Caerwent, suggesting that his diocese covered Gwent. There is evidence that his diocese extended into Ergyng (now south-west Herefordshire). He is recorded in charters dating from the mid-880s to the early tenth century.

In 914 he was captured by the Vikings and ransomed by Edward the Elder, King of the Anglo-Saxons, for 40 pounds of silver. Edward's assistance is regarded by historians as evidence that he inherited the overlordship of his father, Alfred the Great, over the south-east Welsh kingdoms.

Cyfeilliog is probably the author of a cryptogram (encrypted text) in the ninth-century collection of poetry known as the Juvencus Manuscript. Composing the cryptogram would have required knowledge of Latin and Greek. The twelfth-century Book of Llandaff records his death in 927, but some historians are sceptical as they think that this date is late for a bishop active in the 880s.