The Mission to the Slavs
In brief
In the ninth century two brothers from Thessalonica — Constantine, better known by his monastic name Cyril, and Methodius — carried the Gospel to the Slavic peoples of Central Europe. To do it they created the first Slavic alphabet and translated the Scriptures and the services into the people's own language. That choice — that a people should worship in a tongue they understand — became a lasting principle of Orthodox mission.
The brothers from Thessalonica
Constantine and Methodius came from a prominent family in Thessalonica, a great city of the empire ringed by Slavic settlements, so the brothers grew up knowing Slavic speech alongside Greek. Constantine was a brilliant scholar — his contemporaries called him "the Philosopher" — while Methodius had governed a province before withdrawing to a monastery. Both were servants of Byzantium and of its Church.
The brothers were seasoned missionaries before they ever reached the Slavs: Constantine had already been sent on embassies to the Arabs and, with Methodius, to the Khazars north of the Black Sea. So when, in 863, Prince Rastislav of Great Moravia, in the heart of Central Europe, sent to Constantinople asking for teachers who could instruct his people in the Christian faith in their own language, the Emperor Michael III and the Patriarch Photios chose these two. Their great mission to the Slavs began.
An alphabet and a liturgy
The Slavs had no writing of their own. Constantine devised an alphabet for them — the Glagolitic — carefully shaped to the sounds of their speech; from his work his disciples later developed the script we call Cyrillic, named in his honor. With it the brothers translated the Gospel, the Psalter, and the Divine Liturgy into Slavonic, giving the Slavs the whole of Christian worship in words they could understand (see the Slavic alphabets and Church Slavonic).
This provoked fierce opposition from the Frankish clergy already working in the region, who held to a "three-language" theory: that God could be worshiped only in Hebrew, Greek, and Latin — the three tongues Pilate had written over the Cross. The brothers rejected this and appealed to Rome, where Pope Hadrian II approved the Slavonic books. Constantine died in Rome in 869, having taken the monastic name Cyril shortly before; Methodius, consecrated archbishop, carried on until his death in 885. After he died his disciples were driven out of Moravia and found refuge to the south, where the mission bore its richest fruit (see the conversion of Bulgaria and Serbia).
The vernacular principle
The lasting legacy of the brothers was not a single successful mission — that one was largely uprooted in their own lifetime — but a principle: the Church prays best in the language of the people. This was not an innovation but the pattern of Pentecost, when each heard the wonders of God in his own tongue, and of St. Paul, who preferred five words understood to ten thousand in a language no one grasped.
That conviction shaped Orthodox mission ever after, from Slavonic in the ninth century to Aleut and Yupik in Alaska, to Japanese, to English today. It is why the two brothers are honored together as "Equals to the Apostles" and "Enlighteners of the Slavs." From the seed they planted grew the whole Slavic Orthodox world — including, a century later, the baptism of Rus'.