Cyril and Methodius were born in Thessalonika, Greece. The area was inhabited by many Slavic people, and the brothers learned their language. They eventually became priests and were sent to Moravia, a Slav-speaking nation, to preach to people in their own language upon the request of Prince Rostislav.
In 863, the brothers were part of a small group of missionaries sent to Moravia. The group was led by Cyril, and they took with them an invaluable tool: the holy Mass translated into Slavic for the first time. The German-influenced clergy did not accept the missionaries, distrusting the translated liturgy. Catholicism blossomed in the foreign land, and the missionaries soon found themselves in need of more priests. However, without the support of the local clergy, they had no bishop to ordain new priests. They traveled to Rome to appeal to Pope Adrian II, who officially approved the translated liturgy and ordained them both bishops.
While still in Rome, Cyril died on February 14, 869, passing leadership onto his brother. Methodius returned to Moravia, bearing with him a letter of approval from the Pope. However, since his departure, Rostislav had been driven out by his nephew, Svatopluk, who had become an ally of Carloman of Bavaria. The new prince stood against the missionaries. Methodius was imprisoned for two years before the Pope, now John VIII, could procure his release.
Pope John banned the use of the Slavonic language in the liturgy, yet Methodius continued with his mission. His enemies also accused Methodius of heresy. Later, before the Pope, the holy bishop was able to convince him both of his orthodoxy and of the need for the use of Slavonic in the liturgy, which John VIII reinstated with some reservations.
St. Methodius spent the last four years of his life completing the Slavonic translation of the Bible, which suggests that he was prevented from fully exercising his missionary work by the continuous Germanic opposition. Methodius died on April 6, 884, his body exhausted from his apostolic efforts.