Then in 862 the two brothers were invited by Prince Rastislav of Great Moravia to preach Christianity in his domains. This request was a fallout of the efforts of the Slavic princes in central Europe attempting to maintain their independence from their Germanic neighbors. Rastislav was looking for Christian missionaries to replace those from the Germans. In the end this mission would continue for the rest of the brothers' lives, as the brothers were dedicated to the idea that Christianity should be presented to the people in their native languages as was the practice in the East. To accomplish their work they developed the Glagolitic alphabet, the precursor of the Cyrillic alphabet, and began the translation of the [[Scripture]]s and Christian literature into the Slavic language.
The German [[clergy]] had used their liturgical language, Latin, as a measure to maintain their influence in Moravia and therefore were unhappy with the work of Constantine and Methodius, and they used this difference to attack the brothers. After laboring for about four years, the brothers were called by Nicholas I to appear in [[Church of Rome|Rome]] to defend their work. The area in which they worked was within the [[jurisdiction]] of Rome. However, before their arrival, in 869 Nicholas died and was succeeded by Adrian II. After Adrian was convinced of the orthodoxy of the brothers, he approved their use of Slavonic in their church services and commended their work. He then [[Consecration of a bishop|consecrated]] Methodius [[bishop]]. Constantine took monastic vows in a Greek monastery in Rome. He was given the name ''Cyril'', the name by which he is now commonly known. Cyril was not to return to Moravia as he died shortly thereafter. The date of Cyril's death is uncertain, but appears to have been shortly after his consecration, both perhaps in February 869, with his death most probably on [[February 14]].
Adrian II reestablished the old [[diocese]] of Panonia, as the first Slavonic diocese of Moravia and Pannonia, independent of the Germans, at the request of the Slavic princes Rastislav, Svatopluk, and Kocel. Here Methodius was appointed to the new diocese as [[archbishop]]. However, on returning to Moravia in 870, King Louis and the German bishops summoned Methodius to a [[synod]] at Radisbon, where they deposed him and sent him to prison. After the Germans suffered military defeats in Moravia, John VIII freed him three years later and restored Methodius as Archbishop of Moravia. Soon his orthodoxy was again under question by the Germans, particularly over the use of Slavonic. Once again John VIII sanctioned the use of Slavonic in the [[liturgy]] but with the stipulation that the [[Gospel]] must first be read in Latin before the reading in Slavonic. Also, Methodius' accuser, Wiching, was named a [[vicar bishop]] to Methodius, and from this position he continued to oppose him. With his health damaged during his long struggle with his opponents, Methodius died on [[April 6]], 885, after having recommended as his successor his [[disciple]], the Moravian Slav, Gorazd. The brothers are remembered on [[May 11]]. St. Cyril's repose is also commemorated on [[February 14]], and St. Methodius's repose is also commemorated on [[April 6]].