Since the empire was originally the eastern part of the Roman Empire, Latin was the language used at first in government, for church rites, and at the royal court. Greek, however, was the language most widely spoken in the domain; by the mid-seventh century it was the official language, and western Europeans came to call Byzantium the Greek Empire.
The language of the empire was Roman until 7th C, when Heraclius changed to Greek, Latin became only a ceremonial language. The Vulgar Latin effectively spoken in the Thraces later gave birth to Romanian language today. The relations between the eastern and the western churches entered into turmoil of crises in 1054. Three papal legates entered Hagia Sophia on Saturday, 16th July and placed a bull of excommunication on the altar, marking the beginning of centuries lasting separation.
Heraclius ended the use of Latin in government when he made Greek the official language of the Byzantine Empire. Instead of being called by the Latin terms Imperator, Caesar, or Augustus, he was named Basileus, the Greek word for king though in this context it is translated Emperor. He began the Byzantine practice of designating his successor as Co-emperor to give the next Emperor experience and facilitate the succession.
Byzantine was generally known to many of its Western contemporaries as the Empire of the Greeks. This was because of the dominance of Greek language, culture and population. Greek was not only the official language, but also the language of the church, of the literature and of all commercial transactions.
Even though the Byzantine Empire was a multinational state, including Greeks, Armenians, Jews, Egyptians, Syrians, Illyrians, and Slavs, it was considered to be a "Greek state" due to its Orthodox Christian character and its common Greek culture radiated by large centers of Hellenism such as Constantinople, Antioch, Ephesus, Thessalonika and Alexandria.
An archaic style of Greek served as the language of administration and of most writing during the period of the Byzantine, or Eastern Roman, Empire until the fall of Constantinople to the Turks in 1453. During the Byzantine period the spoken language continued to develop without the archaizing tendencies of the written language. Byzantine Greek is still the liturgical language of the Greek Orthodox church.
The Greek language led to a Greek culture. The Byzantine Empire stood out for their Christian religion and their expression of it in their artwork. These Romans carved exquisite ivories, illuminated manuscripts, and formed mosaics out of glass and stone. Mosaics were pictures formed from these objects with the intent to stimulate profound religious thought. The mood of these mosaics was always honoring and respectful of Christianity and its components. Another form of Christian expression was in the form of icons.