This article records tradition as it has been passed down and reported. Its sources are not yet part of the atlas's verified catalogue.
Not everyone welcomed a Christian liturgy conducted in Slavic. When Cyril and Methodius traveled to Venice in 867, on their way to Rome to resolve a jurisdictional dispute with the Latin rite clergy already working in Great Moravia, they were confronted by Frankish churchmen who argued that only three languages, Hebrew, Greek and Latin, the languages named on the inscription over the cross at the crucifixion, could properly be used to worship God. Constantine, who had not yet taken his monastic name of Cyril, answered the challenge directly, citing scripture, including Paul's first letter to the Corinthians on speaking so that a congregation can understand, to argue that no language was intrinsically unfit for praising God. Later writers gave the Frankish position a name, the trilingual heresy, sometimes called the Pilate heresy after the multilingual sign Pilate ordered placed on the cross. The dispute might have ended the brothers' work entirely, but Pope Hadrian II sided with them once they reached Rome, formally approving the Slavic liturgy and reportedly taking part in a service conducted in it himself, a significant endorsement from the one authority the Frankish clergy could not simply override. That papal support did not end the hostility on the ground. After Methodius died in 885, his Frankish rivals moved quickly against his disciples, and many of the Slavic speaking clergy he had trained were driven out of Great Moravia entirely, carrying the Glagolitic alphabet and the Slavic liturgy with them into Bulgaria, where the tradition took root and eventually gave rise to the Cyrillic script that still bears Cyril's name.