Constantine, known as the Philosopher because of his erudition, was Librarian at the Church of the Holy Wisdom in Constantinople; he later became a monk with the name of Cyril. The Emperor Michael sent him with his brother Methodius to the Khazars in response to their petition for teachers to expound to them the Christian Faith. On their way, they stayed in Cherson, where they recovered from the Black Sea the relics of Saint Clement of Rome.
The two brothers were approached in 850 by Saint Photios the Great (see February 6th) to lead a diplomatic mission to the Khazars, the people who inhabited the western shore of the Caspian Sea. Cyril and Methodius accepted this mission and departed to the North. After the success of this trip, the brothers lived for a time in a monastery on Mount Olympus where Methodios became a monk. At this time the brothers utilized their childhood Slavonic education to develop a written alphabet for the Slavonic language, which to this time had never existed. This alphabet became known as the Glagolitic Alphabet. On their own instigation, the brothers began translating the Gospels and liturgical service books into Slavonic.
Later, they were called by Prince Rostislav of Moravia to instruct his people in the Orthodox Faith (Saint Rostislav died a martyr's death and is celebrated Oct. 15). In their apostolic labours throughout the Balkans, the holy brothers were slandered by certain Germanic bishops who opposed the use of the vernacular in the church services. After five years of service, the brothers made their way to Rome in 867 to have members of their company ordained to the priesthood to aid in the missionary journey. The presented their Slavonic translations to Pope Adrian II, who received them with love and full approval. The group of missionaries celebrated the Divine Liturgy in Rome in the Slavonic language for the very first time with members of their party being ordained as they intended. Two years later, Saint Cyril reposed in Rome on February 14 and was buried in the Church of Saint Clement.
Saint Methodius was made Bishop of Moravia, but at the intrigues of certain Latin clergy, was cast into prison by the "Holy Roman Emperor" (the Germanic Emperor of the West), where he was cruelly tormented for some three years. In 874, through the defense of Pope John VIII, he was freed and made Archbishop of Moravia. Because he reproved the lax morals of the German priests in Moravia, he was soon accused of heresy by them, and was forbidden to celebrate the Liturgy in Slavonic. Summoned to Rome again in 879, he was completely exonerated and allowed once again to use the Slavonic tongue for the divine services. He reposed on April 6, 885.
Saint Cyril was from Alexandria, born about the year 376. He was the nephew of Theophilus, Patriarch of Alexandria, who also instructed the Saint in his youth. Having first spent much time with the monks in Nitria, he later became the successor to his uncle's throne in 412. In 429, when Cyril heard tidings of the teachings of the new Patriarch of Constantinople, Nestorius, he began attempting through private letters to bring Nestorius to renounce his heretical teaching about the Incarnation. When the heresiarch did not repent, Saint Cyril, together with Pope Celestine of Rome, led the Orthodox opposition to his error. Saint Cyril presided over the Third Ecumenical Council of the 200 Holy Fathers in the year 431, who gathered in Ephesus under Saint Theodosius the Younger. At this Council, by his most wise words, he put to shame and convicted the impious doctrine of Nestorius, who, although he was in town, refused to appear before Patriarch Cyril. Saint Cyril, besides overthrowing the error of Nestorius, has left to the Church full commentaries on the Gospels of Luke and John. Having shepherded the Church of Christ for thirty-two years, he reposed in 444.