Cyril and Methodios
Cyril (b. Thessalonike, 827-d. Rome, 869) and Methodios (b. Thessalonike, 815-d. Velegrada, Moravia, 885), scholars, missionaries to the Slavs and later saints, were two of the most important figures of Byzantium.

Cyril (baptized Constantine) studied in Thessalonike, where his father Leon was a military governor, and at the university of Constantinople. He was a member of Leon the Mathematician's circle and of Photios' and may have taught "philosophy to both natives and foreigners". By contrast, his eldest brother Methodios, following studies in Thessalonike, was appointed "governor of a Slav principality".

The linguistic abilities of both brothers and Cyril's profound knowledge of religious questions explain why they were chosen by the Byzantine authorities to undertake religious missions to alien peoples (in 851 to the Arabs, and to the land of the Khazars on the Caspian Sea).

When Rastislav, ruler of the Slavs of Greater Moravia (present-day Czechia and Slovakia), invited Byzantium to send a mission to his people, the political and ecclesiastical authorities in Constantinople, recognizing the diverse benefits that might flow from such a step, dispatched the two brothers with a view to propagating Christianity and establishing the new Church.

Cyril introduced the first alphabet of Slavonic (the Glagonic alphabet) and with Methodios' help translated not only the Holy Scripture but also the liturgies into Slavonic. These works became the cornerstone of Slav literature.

Despite the difficulties presented by opposition from western clergy and Frankish suzerainty over Moravia, the two missionaries established the Christian faith and instructed students and Church leaders drawn from the local population.

On their return from Moravia they accepted an invitation from the ruler of Pannonia (present-day Hungary) Kotsel, a vassal of the Franks, to visit and preach to his people. They visited Rome where the pope Adrian II endorsed their work.

The younger brother, Constantine, died in Rome in 869, after he had received the tonsure as the monk Cyril, while Methodios was consecrated by the Pope bishop of Pannonia with his see at Sirmium.

Hardening reaction on the part of western clergy and a shift in policy by Sviatopolk, Rastislav's nephew and heir, led to the arrest of Methodios and his transfer to the eastern Frankish state (present-day Germany) where he was condemned to penal servitude for life. Two years later Methodios was released and despite opposition from western clerics, was consecrated bishop of Moravia in 880.

Until his death in 885 Methodios was engaged in writing and translating. Although he had settled upon his successor, Frankish clergy succeeded in expelling his students, who took refuge in Bulgaria. There they carried on the work of their teachers under the leadership of Saint Clement and his disciple Naum.