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Traditionally, Erbin was a King of Dumnonia, the son of Constantine Corneu and the father of Geraint. He chiefly appears in Geraint and Enid, one of the Three Welsh Romances of the Mabinogion. In the romance of Culhwch and Olwen he or another Erbin is made the father of Dywel, Gereint and Ermid.
In the Mabinogion he appears as an old king whose realm is subject to attacks from his enemies. He recalls his son from the court of King Artu to aid him in the war and restores the Dumnonian power, then abdicates in his son's favour. About 480 Erbin dies.
Erbin appears as a saint in the Bonedd y Saint and is traditionally associated with Erbistock in Denbighshire. His feast day is 13 January. Gilbert Hunter Doble suggested he might be the same as Saint Ervan/Erme of Cornwall.
Erbyn or Ervan is said to have been the father of Selevan. Erbyn is the original patron saint of St Ervan but in more modern times he has become confused with the Greek saint Hermes who is now regarded as such.
He was probably the founder of the church of Saint Ervan in Cornwall. In ancient Welsh calendars he is commemorated as a saint on 13 January or 29 May.
- Ford, David Nash. "Erbin, King of Dumnonia". Early British Kingdoms. Retrieved 21 February 2012.
- Doble, G. H. (1965) "Note, Saint Hermes" D. Attwater, in: The Saints of Cornwall; Part 4: saints of the Newquay, Padstow and Bodmin district. Truro: Dean and Chapter; p. 167
- Ellis, P. B. (1992) The Cornish Saints. Penryn: Tor Mark Press; p. 11