These two celebrated apostles of the East are bound by more than one tie to the history of Papal Rome. The Slav nations are indebted to Cyril and Methodius for their civilization, their faith, and their original communion with the See of Peter. To this day the Slav pilgrim who visits Rome and kneels at the sepulcher of the Prince of the Apostles sees upon that tomb a painting representing the Savior between St. Peter and St. Paul. That venerated icon, on which is traced an inscription in the Slavonic tongue, is said to have been placed there by Sts. Cyril and Methodius as a mark of their homage and devotion to the Apostolic See.
They were consecrated bishops by Pope Adrian II. They invented a writing for the language of the Slav; translated the Scriptures and made use of this language in the Liturgy. Cyril, worn out by the mission, returned to Rome and prepared a tomb for himself in the shadow of St. Clement’s. He died in 869 at the age of 42. Methodius died in 885.
(Source: The New Roman Missal, Rev. F. X. Lasance)