As the 9th-century missionaries Saints Cyril and Methodius undertook their mission to evangelize to the Slavs of Great Moravia, two writing systems were developed: Glagolitic and Cyrillic. Both scripts were based on the Greek alphabet and share commonalities, but the exact nature of relationship between the Glagolitic alphabet and the Early Cyrillic alphabet, their order of development, and influence on each other has been a matter of great study, controversy, and dispute in Slavic studies.