The origin of the Albanians has been the subject of historical, linguistic, archaeological and genetic studies. Albanians continuously first appear in the historical record in Byzantine sources of the 11th century. At this point, they were already fully Christianized. Albanian forms a separate branch of Indo-European, first attested in the 15th century, having evolved from one of the Paleo-Balkan languages of antiquity. The surviving pre-Christian Albanian culture shows that Albanian mythology and folklore are of Paleo-Balkanic origin and that almost all of their elements are pagan.