3 The brothers Cyril and Methodius, born in Thessalonica, went as boys to Constantinople in order to study the humanities in the chief city of the East. The spark of genius already discerned in these young men soon became apparent. They both advanced quickly, especially Cyril, who became so distinguished in learning that he won for himself the title of "The Philosopher." Soon after this, Methodius undertook the monastic life. Under the influence of the Patriarch Ignatius, the Empress Theodora commissioned Cyril to teach the Christian faith to the Khazer tribes who dwelt beyond the Chersonese. These people had asked that suitable priests might be sent to them from Constantinople. Cyril accepted the mission willingly and departed for Tauric Chersonese so that, as some relate, he could study the language of the people. It was at this time that he had the good fortune to discover the remains of Pope Clement I. This courageous martyr was thrown into the sea by order of the Emperor Trajan and was afterwards buried with the anchor to which he had been fastened. The anchor, together with the ancient tradition, made it very easy to identify the remains. With this priceless treasure, Cyril went into the towns and homes of the Khazars. In a short time, after abolishing many superstitions, he won for Jesus Christ these people, who were taught by his word and moved by the spirit of God. To the new Christian community Cyril gave an example of self control and charity by refusing all the gifts offered to him by the inhabitants, except the slaves whose liberty he restored to them when they embraced Christianity. He soon returned to Constantinople to enter the monastery of Polychronius, which Methodius had entered.
Source: Grande Munus (Vatican.va)