Greek East and Latin West are terms used to distinguish between the two parts of the Greco-Roman world and of Medieval Christendom, specifically the eastern regions where Greek was the lingua franca and the western parts where Latin filled this role.
Greek had spread as a result of previous Hellenization, whereas Latin was the official administrative language of the Roman state, stimulating Romanization. In the east, where both languages co-existed within the Roman administration for several centuries, the use of Latin ultimately declined as the role of Greek was further encouraged by administrative changes in the empire's structure between the 3rd and 7th centuries, which led to the split between the Eastern Roman Empire and the Western Roman Empire, the collapse of the latter, and failed attempts to restore unity by the former. This Greek–Latin divide continued with the East–West Schism of the Christian world during the Early Middle Ages.
