Cyril and Methodius, the apostles of the Slavs, were brothers who hailed from Thessalonia. After receiving an excellent education, they were sent by the Eastern Emperor Michael III (842-856) into the kingdom of Grand-Moravia; through great effort and in spite of tremendous difficulties they converted the Slavonic nations.

They translated the Bible into Slavonic and devised a kind of writing, called glagolitic, which even to the present day is used in the liturgical services of some Eastern rites.

In 867 the two brothers came to Rome, were met by Pope Hadrian II (867-872) and the whole papal court. They gave a report of their labours, but encountered opposition on the part of jealous clergy who took offence, it was said, because of their liturgical innovations. Cyril and Methodius explained their methods and from the Pope himself received episcopal consecration (868).

Soon after, Cyril died at Rome, only forty-two years old, and was buried in St. Peter's; later his body was transferred to San Clemente, where his remains still rest. His funeral resembled a triumphal procession.

Methodius returned to Moravia and laboured as a missionary among the Hungarians, Bulgarians, Dalmatians, and the inhabitants of Carinthia. Falling again under suspicion, he returned to Rome and defended the use of the Slavonic language in the liturgy.

The Pope bestowed upon him the dignity of archbishop. After his return to Moravia, he converted the duke of Bohemia and his wife, spread the light of faith in Bohemia and Poland, is said to have gone to Moscow (after the erection of the See of Lemberg), and to have established the diocese of Kiev. After his return he died in Bohemia and was buried in the Church of St. Mary at Velehrad, the services being conducted in Greek, Slavonic, and Latin.