28 It is fitting, then, that the Church should celebrate with solemnity and joy the eleven centuries that have elapsed since the close of the apostolic work of the first Archbishop, ordained in Rome for the Slav peoples, Methodius, and of his brother Cyril, and that she should thus commemorate the entry of these peoples on to the scene of the history of salvation and into the of European nations which during the preceding centuries had already accepted the Gospel message. Everyone will understand with what profound happiness I will share in this celebration as the first son of the Slav race to be called, after nearly two millennia, to occupy the episcopal see that once belonged to Peter in this city of Rome.
Source: Slavorum Apostoli (Vatican.va)