The time came when the Duke of Moravia (the present-day Czech Republic) received political independence from German rule, and also received ecclesiastical autonomy, which meant having their own clergy and their own form of the liturgy. It was in these circumstances that Cyril and Methodius became missionaries, devoting themselves to spreading the Gospel and to strengthening the Church among the Slavic people.
Cyril's first work was to invent an alphabet, still used in some Eastern liturgies. The Cyrillic alphabet was formed, being based on Greek capital letters. Together the brothers translated the Gospels, the psalter, St. Paul's epistles, as well as the liturgical books, into Slavonic. They composed a Slavonic liturgy, which was very unusual at that time, since the expectation was that the liturgy would be unified with the liturgy of the Western Church, and would use Latin as its language.
Because of these liturgical differences, the use of a different alphabet, and their free use of the vernacular in preaching, it led to opposition from the German clergy. The bishop refused to consecrate Slavic bishops and priests, and Cyril was forced to appeal to Rome. On their visit to Rome, he and Methodius had the joy of seeing their new liturgy approved by Pope Adrian II. Cyril died during this visit to Rome, and is buried at San Clemente, but Methodius continued his mission work for 16 more years. There were still many in the Church who fought against what the brothers had been doing, and it seemed as though their efforts would die with them. However, the Slavic people held on to their liturgy and their language, and it continued to spread, as it has done to this day.
Almighty and everlasting God, we thank thee for thy servants Cyril and Methodius, whom thou didst call to preach the Gospel to the Slavic peoples: raise up, we pray thee, in this and every land, heralds and evangelists of thy kingdom; that thy Church may make known the unsearchable riches of Christ, and may increase with the increase of God; through the same Jesus Christ thy Son our Lord, who liveth and reigneth with thee, in the unity of the Holy Spirit, ever one God, world without end. Amen.