Slavic mythology or Slavic paganism or Slavic religion describes the religious beliefs, myths and ritual practices of the Slavs before the formal Christianisation of their ruling elites. The latter occurred at various stages between the 8th and the 13th century: The South Slavs living on the Balkan Peninsula in South Eastern Europe, bordering with the Byzantine Empire to the south, came under the sphere of influence of Eastern Orthodox Christianity, beginning with the creation of the Slavic alphabet (first Glagolitic, and then Cyrillic script) in 855 by the brothers Saints Cyril and Methodius and the adoption of Christianity in Bulgaria in 863 AD. The East Slavs followed with the official adoption in 988 AD by Vladimir the Great of Kievan Rus'.
The West Slavs came under the sphere of influence of the Roman Catholic Church starting in the 12th century, and Christianisation for them went hand in hand with full or partial Germanisation.
The Christianisation of the Slavic peoples was, however, a slow and—in many cases—superficial phenomenon, especially in what is today Russia. Christianisation was vigorous in western and central parts of what is today Ukraine, as they were closer to the capital Kiev, but even there, popular resistance led by volkhvs, pagan priests or shamans, recurred periodically for centuries.
The West Slavs of the Baltic withstood tenaciously against Christianity until it was violently imposed on them through the Northern Crusades. Among Poles and East Slavs, rebellion outbreaks occurred throughout the 11th century. Christian chroniclers reported that the Slavs regularly re-embraced their original religion (relapsi sunt denuo ad paganismus).
Many elements of the indigenous Slavic religion were officially incorporated into Slavic Christianity, and, besides this, the worship of Slavic gods has persisted in unofficial folk religion until modern times. The Slavs' resistance to Christianity gave rise to a "whimsical syncretism" which in Old Church Slavonic vocabulary was defined as dvoeverie, "double faith". Since the early 20th century, Slavic folk religion has undergone an organised reinvention and reincorporation in the movement of Slavic Native Faith (Rodnovery).