Reginhar, Bishop of Passau in the context of Roman Catholic Archdiocese of Salzburg

The Christianization of Moravia refers to the spread of the Christian religion in the lands of medieval Moravia (Great Moravia).

What modern historians designate as Great Moravia was a Slavic state that existed in Central Europe from around 830 to the early 10th century. The territory of Great Moravia was originally evangelized by missionaries coming from the Frankish Empire or Byzantine enclaves in Italy and Dalmatia since the early 8th century and sporadically earlier. The diocese of Passau was charged with establishing a church structure in Moravia. The first Christian church of the Western and Eastern Slavs known to the written sources was built in 828 by Pribina, the ruler and Prince of the Principality of Nitra, although probably still a pagan himself, in his possession called Nitrava (today Nitra, Slovakia). The first Moravian ruler known by name, Mojmír I, was baptized in 831 by Reginhar, Bishop of Passau. Due to internal struggles between Moravian rulers, Mojmir was deposed by Rastislav in 846; as Mojmir was aligned with Frankish Catholicism, Rastislav asked for support from the Byzantine Empire and aligned himself with Eastern Orthodoxy.