The Byzantine Empire

The Byzantine Empire, sometimes known as the Eastern Roman Empire, was the predominantly Greek-speaking continuation of the eastern half of the Roman Empire during Late Antiquity and the Middle Ages. Its capital city was Constantinople (modern-day Istanbul), originally founded as Byzantium. It survived the 5th century fragmentation and fall of the Western Roman Empire and continued to exist for an additional thousand years until it fell to the Ottoman Turks in 1453. During most of its existence, the empire was the most powerful economic, cultural, and military force in Europe. Both "Byzantine Empire" and "Eastern Roman Empire" are historiographical terms created after the end of the realm; its citizens continued to refer to their empire as the Roman Empire.

Several events from the 4th to 6th centuries mark the transitional period during which the Roman Empire 's east and west divided. In 285, the emperor Diocletian (r. 284–305) partitioned the Roman Empire 's administration into eastern and western halves. The borders of the Empire evolved significantly over its existence, as it went through several cycles of decline and recovery. During the reign of Justinian I (r. 527–565), the Empire reached its greatest extent after reconquering much of the historically Roman western Mediterranean coast, including north Africa, Italy, and Rome itself, which it held for two more centuries. During the reign of Maurice (r. 582–602), the Empire 's eastern frontier was expanded and the north stabilized. However, his assassination caused a two-decade-long war with Sassanid Persia which exhausted the Empire 's resources and contributed to major territorial losses during the Muslim conquests of the 7th century. In a matter of years the Empire lost its richest provinces, Egypt and Syria, to the Arabs.

The final centuries of the Empire exhibited a general trend of decline. It struggled to recover during the 12th century, but was delivered a mortal blow during the Fourth Crusade, when