There are few events in history which had such a profound influence on the cultural development of so many nations as had the Byzantine mission to Moravia. Although the mission failed in the country for which it had been destined, the work of the two Greek brothers, aided by a few disciples, produced unexpected fruit among the Bulgarians, Serbians, Croats, and Eastern Slavs, and became the basis of the oldest Christian Slavic culture. This shows us the excellence of the first literary achievements in Moravia and testifies to the geniality of the inventor of the Slavic alphabet, and to Constantine’s extraordinary philological talent. A mediocre work could not have survived the Moravian catastrophe and the many upheavals in the early history of the southern and eastern Slavs.