The Celtic mythology of Wales has been more corrupted by the dominant presence of non-Celtic people (e.g., Romans, Saxons, English) than the Celtic mythology of the more isolated island of Ireland. Two Latin texts concerned primarily with the Arthurian stories are the early ninth-century Historia Brittonum by Nennius and the twelfth-century Historia Regum Britanniae by Geoffrey of Monmouth. And there are oral sources, including, traditionally, poems attributed to the almost certainly mythic sixth-century poet-prophet Taliesin, the Welsh equivalent of the Irish Amairgen. The major source for Welsh mythology, however, is a medieval collection of tales known to us as the Mabinogion (Mabinogi).