In Late Antiquity times and during the Middle Ages the Byzantine Empire was started as an extension of the Roman Empire and the chief language spoken was Greek. The capital city was Constantinople although it was originally known as Byzantium and is today modern Istanbul . Primarily it was the Eastern Roman Empire that had survived a 5th century division after the Western Empire collapsed. The Empire went on to flourish for a further 1,000 years until it succumbed to the Ottoman Turks in 1453 and in its time was the most powerful in Europe in terms of military force, economy and culture.
The names Byzantine Empire and Eastern Roman Empire are in fact historical terms that were applied in later centuries; the actual people who lived there always referred to the empire as the “Roman Empire”.
There were several events that occurred between the 4th and 6th centuries that marked transitional times when the East and West Roman Empires became divided; in 285 Emperor Diocletian (284-305) split the Empire’s administration between the eastern and western sides; then Constantine (306-337) in 330 transferred the chief capital from Rome to Byzantium which became known as the “City of Constantine” (Constantinople) and “Nova Roma” (New Rome); then Christianity was introduced as the Empire’s official religion under Theodosius I (379-395) who banned all other Roman religions and finally Heraclius (610–641) reorganised the administration and military and implemented the use of the Greek language over Latin which went on to distinguish it from ancient Rome, becoming an empire of Greek culture and Orthodox Christianity.
The Empire’s borders grew tremendously going through several stages of decline and recovery. It was during the reign of Justinian I (527–565) that the Empire reached its greatest magnitude after retaking large parts of what was historically the Roman Western Mediterranean coastline that included North Africa, Italy and Rome and managed to control them for over two centuries.
The Eastern frontier of the Empire was expanded north and stabilised by Emperor Maurice (582–602) but after he was assassinated a 20 year long battle ensued with Sassanid Persia which contributed to major land losses during the Islamic conquests in the 7th century and exhausted much of the Empire’s resources. In the 10th century, during the Macedonian dynasty, the Empire recovered but after 1071 lost much of Asia Minor to the Seljuk Turks.
The final centuries of the Byzantine Empire continued to decline and although it fought to recover in the 12th century it was finally defeated by the Fourth Crusaders who destroyed Constantinople and divided the Empire into competing Byzantine Greek and Latin dominions. Byzantium recovered and the Empire was re-established in 1261 continuing for a further 200 years but only as one of many rival states in the area. This explosive period lead to its reformist occupation in the 15th century by the Ottomans and on to the eventual “Fall of Constantinople” in 1453.