Cultural development resulted from the mission of Saints Cyril and Methodius, who came during the reign of Prince Rastislav in 863. The empire reached its greatest territorial extent under Svatopluk I (871–894), although the borders of his dominions are still under debate. He also received a letter from by Pope John VIII who styled him "king" Svatopluk.
Weakened by internal struggle and frequent wars with the Carolingian Empire, Great Moravia was ultimately overrun by the Hungarians, who invaded the Carpathian Basin around 896. Its remnants were divided between Poland, Hungary, Bohemia and the Holy Roman Empire. Although some contemporary sources mention that Great Moravia vanished and the Moravian castles were abandoned for a century, archaeological research and toponyms suggest that there was continuity in the Slavic population in the valleys of the rivers of the Inner Western Carpathians. Most castles and towns survived the destruction of the state, but the identification of some castles is still debated and some scholars even claim that Great Moravia disappeared without trace.
Great Moravia left behind a lasting legacy in Central and Eastern Europe. The Glagolitic script and its successor Cyrillic were disseminated to other Slavic countries, charting a new path in their cultural development. The administrative system of Great Moravia may have influenced the development of the administration of medieval Hungary. Great Moravia also became a favorite issue in the Czech and Slovak romantic nationalism of the 19th century.
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