The moment
Two brothers from Thessalonica, sent by Emperor Michael III at the request of Prince Rastislav of Moravia, began preaching in Slavonic in 863. Cyril devised an alphabet, Glagolitic, and the brothers translated scripture and the liturgy, which Pope Adrian II approved in Rome. German bishops fought the Slavonic rite, and after Methodius died their disciples were driven out to Bulgaria, where the Cyrillic alphabet was created.
People: Cyril (Constantine), Methodius, Rastislav of Moravia