The origin of the Albanians has long been a matter of debate within scholarship. The Albanians first appear in the historical record in Byzantine sources of the 11th century. At this point, they were already fully Christianized. The Albanian language forms a separate branch of Indo-European, first attested in the 15th century, and is considered to have 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.