Monotheism

====Ancient proto-Indo-European religion====
{{main|Proto-Indo-European religion}}
The head deity of the [[Proto-Indo-European religion]] was the god [[Dyeus|*''Dyḗus Pḥ<sub>a</sub>tḗr '']]. A number of words derived from the name of this prominent deity are used in various [[Indo-European languages]] to denote a monotheistic God. Nonetheless, in spite of this, Proto-Indo-European religion itself was not monotheistic.<ref>{{cite book|last1=Mallory|first1=J. P.|last2=Adams|first2=D.Q.|title=The Oxford Introduction to Proto-Indo-European and the Proto-Indo-European World|date=2006|publisher=Oxford University Press|location=Oxford, England|isbn=978-0-19-929668-2|pages=408–411 and 423–434}}</ref>

In [[Eastern Europe]], the ancient traditions of the Slavic religion contained elements of monotheism. In the sixth century AD, the Byzantine chronicler [[Procopius]] recorded that the Slavs "acknowledge that one god, creator of lightning, is the only lord of all: to him do they sacrifice an ox and all sacrificial animals."<ref name=katicic2008>{{cite book |last=Katičić |first=Radoslav |title=Božanski boj: Tragovima svetih pjesama naše pretkršćanske starine |year=2008 |publisher=IBIS GRAFIKA |location=Zagreb |isbn=978-953-6927-41-8 |url=http://ir.nmu.org.ua/bitstream/handle/123456789/120570/96db5654f2d3025b46454ace91716506.pdf |ref=Katičić 2008 |url-status=dead |archive-url=https://web.archive.org/web/20151018000746/http://ir.nmu.org.ua/bitstream/handle/123456789/120570/96db5654f2d3025b46454ace91716506.pdf |archive-date=2015-10-18 }}</ref> The deity to whom Procopius is referring is the storm god [[Perún]], whose name is derived from [[Perkwunos|*''Perk<sup>w</sup>unos'']], the Proto-Indo-European god of lightning. The ancient Slavs syncretized him with the Germanic god [[Thor]] and the Biblical prophet [[Elijah]].<ref>{{citation|last1=Puhvel|first1=Jaan|author-link=Jaan Puhvel|title=Comparative Mythology|date=1987|publisher=Johns Hopkins University Press|location=Baltimore, Maryland|isbn=0-8018-3938-6|pages=234–235}}</ref>