Old Church Slavonic or Old Slavonic (/sləˈvɒnɪk, slæˈ-/) was the first Slavic literary language. Historians credit the 9th-century Byzantine missionaries Saints Cyril and Methodius with standardizing the language and using it in translating the Bible and other Ancient Greek ecclesiastical texts as part of the Christianization of the Slavs. It is thought to have been based primarily on the dialect of the 9th-century Byzantine Slavs living in the Province of Thessalonica (in present-day Greece).