Cyril (c. 826-869), also known as Constantine, and his brother Methodius (c.815-885) served as Byzantine Christian missionaries to the Slavs in the ninth century. They were Greek brothers born into the Slavic speaking community of Saloniki in Macedonia. In his youth, Constantine attended the imperial university and studied under the leading teachers of the region, including Photius who would later become patriarch of Constantinople. Meanwhile, Methodius became a governor of a Slavic-speaking district until he withdrew into a Greek monastery in Bithnyia. In 851, Constantine went on a four-year mission to the Saracens by the request of the Muslim caliph, after which he joined his brother Methodius at the monastery in 855. Three years later, the brothers received a new assignment from Emperor Michael in Constantinople to go to the land of the Khazars, northeast of the Black Sea. They made a stop in Chersonesus to prepare for the upcoming mission, and according to tradition, Constantine discovered the relics of Saint Clement during their stay in Chersonesus, which he would later give as a gift to Pope Adrian II. The mission that followed was a successful one; it is reported that 200 Khazars were converted and baptized because of the brothers' work.
Following the mission, the brothers returned to Constantinople. The brothers spent their energy translating scriptural and liturgical texts into the Slavic language. At this time, Constantine also composed a totally new Slavonic alphabet that he called the Glagolitic language. In it's final form Glagolitic is known as the Cyrillic alphabet and is still used today by Orthodox Christians in Russia, the Ukraine, Belarus, Bulgaria, and Serbia. Constantine used Glagolitic to translate the Gospels, the epistles of Paul and the Psalms into Slavic.In 862 Prince Rastislav of Moravia sent a request for missionaries to Emperor Michael in Constantinople saying, "Our nation is baptized and yet we have no teacher to direct and instruct us and interpret the sacred scriptures. We understand neither Greek nor Latin. Some teach us one thing and some another. Furthermore, we do not understand written characters nor their meaning. Therefore send us teachers who can make known to us the words of the scriptures and their sense (The Russian Primary Chronicle)". The emperor, despite Constantine's failing health, chose to send Constantine and Methodius to Moravia in 863.
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Constantine's reply was recorded in the Vita of Constantine as being such, "I am weak and sick, but I am happy to go naked and barefoot and I am ready to die for the Christian faith." The brothers worked in the court of the prince of Moravia for three years where they trained the clergy, instructed the people in the Slavonic language, converted the heathen, confirmed those who already were believers in Christian faith and morals, and translated liturgical textbooks into the people's language.Difficulties arose in 864 when Louis the German conquered Moravia, and the Frankish clergy curtailed the activity of the brothers. These people were what Constantine referred to as "trilingualists", meaning they believed that only Latin, Greek, and Hebrew were acceptable for worship. This sect based their belief on the inscription that hung over Jesus' head when he was crucified which identified him "King of the Jews" in Latin, Greek, and Hebrew.As a result of this opposition, Constantine and Methodius journeyed to Rome in 867 with the intent of winning over papal support of their work.
By the time they reached Rome a new pope, Adrian II was in place. Rome received the brothers cordially, especially because they bore the relics of Clement. Adrian gave his approval to the Slavonic translations of both the Bible and the liturgy, blessed the Slavonic books in a service at the altar of the church of the Virgin, and authorized the use of Slavonic in the mass in several churches in Rome in which he installed Methodius and three of his disciples as priests.The brothers did not return to Moravia together because of Constantine's worsening health. Constantine was tonsured as a monk and took on the name of Cyril 50 days before his death on February 14, 869. In the same year, Methodius was consecrated as archbishop of Sirmium in Moravia. But in 870, a new prince came into rule and had Methodius arrested and imprisoned until three years later when Pope John VIII freed him. Methodius continued to face Frankish opposition concerning the Slavic liturgy until his death on April 6, 885.
The heritage of liturgy in the vernacular left by Saints Cyril and Methodius to Eastern Christendom is of great importance. Orthodox churches commemorate Cyril on February 14th, Methodius on April 6th and the brothers together on May 11th. Catholic churches commemorate them together on July 7th.
Encyclopedia of Religion, v. 4, pp. 197-198
The Primary Chronicle, "The Laurentian Text", pp. 63-64
The Dictionary of the Middle Ages, v. 4, pp. 73-74
Modern Encyclopedia of Religions in Russia and Eurasia, v. 6, pp.48-51
Oxford Dictionary of the Christian Church, p.444