The origins of the Cimmerians stretch back to the Thurian Age. The Cimmerians are the descendants of colonists from Atlantis. Living on the main Thurian continent, the colonists survived the great cataclysm which submerged Atlantis and destroyed most of the Thurian civilizations. The survivors, at this point reduced to a stone-age level of sophistication, eventually found themselves locked in multigenerational warfare with survivors of a Pictish colony. This prolonged conflict caused the Atlanteans to further devolve into little more than ape-men. With no memory of their history or even of language and civilization itself, these beings eventually redeveloped into a people known as Cimmerians.
In his essay The Hyborian Age, Howard states that "the Gaels, ancestors of the Irish and Highland Scotch, descended from pure-blooded Cimmerian clans," and he names Conan with a Celtic name. Also, Howard portrays him cursing by Celtic gods.