6 Saint Methodius remained faithful to the words which Cyril had said to him on his deathbed: "Behold, my brother, we have shared the same destiny, ploughing the same furrow; I now fall in the field at the end of my day. I know that you greatly love your Mountain; but do not for the sake of the Mountain give up your work of teaching. For where better can you and salvation?" Consecrated Archbishop for the territory of the ancient Diocese of Pannonia, and named Papal Legate "ad gentes" (for the Slav peoples), he assumed the ecclesiastical title of the re-established Episcopal See of Sirmium. However, Methodius' apostolic activity was cut short as the result of political and religious complications which culminated in his imprisonment for two years, on the charge of having invaded the episcopal jurisdiction of another. He was set free only on the personal intervention of Pope John VIII. The new sovereign of Greater Moravia, Prince Svatopluk, also subsequently showed hostility to the work of Methodius. He opposed the Slavonic liturgy and spread doubts in Rome about the new Archbishop's orthodoxy. In the year 880 Methodius was called ad limina Apostolorum, to present once more the whole question personally to John VIII. In Rome, absolved of all the accusations, he obtained from the Pope the publication of the Bull Industriae Tuae, which, at least in substance, restored the prerogatives granted to the liturgy in Slavonic by Pope John's predecessor Hadrian II. When in 881 or 882 Methodius went to Constantinople, he received a similar recognition of perfect legitimacy and orthodoxy also from the Byzantine Emperor and the Patriarch Photius, who at that time was in full communion with Rome. He devoted the last years of his life principally to making further translations of the Sacred Scriptures, the liturgical books, the works of the Fathers of the Church and also the collection of ecclesiastical and Byzantine civil laws called the Nomocanon. Concerned for the survival of the work which he had begun, he named as his successor his disciple Gorazd. He died on 6 April 885 in the service of the Church established among the Slav peoples.
Source: Slavorum Apostoli (Vatican.va)