Thessalonicean Brothers Cyril and Methodius International Sources on Saints Cyril and Methodius being Greeks. 1. The Columbia Encyclopedia, Sixth Edition. 2001-05: (Cyril and Methodius, Saints) 869 and 884, respectively, GREEK missionaries, brothers, called Apostles to the Slavs and fathers of Slavonic literature. 2. Encyclopedia Britannica, a dictionary of arts, sciences, literature and general information: Saints Cyril and Methodius: ...