Anointed bishops by Pope Adrian II (Introit, Epistle, Alleluia), they converted the Slavonic nations (Collect). To them is attributed the Slav alphabet: into which tongue they translated the Scriptures and celebrated the sacred rites. St. Cyril died in 869 and was buried at Rome near the relics of St. Clement, which he had brought from Chersonesus. St. Methodius died in 885.
Sacerdotes tui, Domine, induant justitiam, et sancti tui exsultent: propter David servum tuum, non avertas faciem Christi tui. * Memento, Domine, David et omnis mansuetudinis ejus.
Let Thy priests, O Lord, be clothed with justice, and let Thy saints rejoice: for thy servant David's sake, turn not away the face of Thy anointed. * O Lord, remember David and all his meekness.
(Psalm 131:9-10,1 from the Introit of Mass)
Omnipotens sempiterne Deus, qui Slavoniae gentes per beatos Confessores tuos atque Pontifices Cyrillum et Methodium ad agnitionem tui nominis venire tribuisti: praesta: ut, quorum festivitate gloriamur, eorum consortio copulemur.
Almighty and everlasting God, who, by the ministry of Thy blessed confessors and bishops Cyril and Methodius, wast pleased to bring the nations of Slavonia to the knowledge of Thy name: grant that we who glory in keeping their festival may have fellowship with them for evermore.(Collect)
From the Catholic Encyclopaedia: http://www.newadvent.org/cathen/04592a.htm