Slavic paganism or Slavic religion describes the religious beliefs, myths and ritual practices of the Slavs before Christianisation, which occurred at various stages between the 8th and the 13th century. The South Slavs, who likely settled in the Balkan Peninsula during the 6th–7th centuries AD, bordering with the Byzantine Empire to the south, came under the sphere of influence of Eastern Orthodox Christianity, beginning with the creation of writing systems for Slavic languages (first Glagolitic, and then Cyrillic script) in 855 by the brothers Saints Cyril and Methodius and the adoption of Christianity in Bulgaria in 863. The East Slavs followed with the official adoption in 988 by Vladimir the Great of Kievan Rus'.
The West Slavs' process of Christianization was more gradual and complicated. The Moravians accepted Christianity as early as 831, the Bohemian dukes followed in 845, but the Poles accepted it much later, in 966, around the same time as the Sorbs, and the Polabian Slavs only came under the significant influence of the Roman Catholic Church from the 12th century onwards. For them and the Sorbs, Christianisation went hand in hand with full or partial Germanisation.[dubious ]
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, since they were closer to the capital, Kyiv. Even there, however, popular resistance led by volkhvs, pagan priests or shamans, recurred periodically for centuries.
The West Slavs of the Baltic tenaciously withstood Christianity until it was violently imposed on them through the Northern Crusades. Among Poles and East Slavs, rebellions broke out 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 (which manifested itself in the architecture of the Russian Church, icon painting, etc.), 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).