Greek culture and language survived in a form of the Byzantine Empire (after the fall and the following decline of Rome) where Greek was the state, liturgy and predominantly spoken language.

Even before the Great Schism of 1054, Greek had been the language used to spread Christianity across southern and eastern Europe, i.e. across the Slavs. Even though the bible was always translated into a local language, Greek retained its prominence in the local education, hence the historical dominance (as opposed to Latin which didn't come into light until after the Renaissance and the spread of the scientific thought all over Europe).