The empire in 555 AD
|-||Roman Empire split||17 January 395|
|-||Empire abolished||13 February 1801|
|Currency||Solidus, denarius and hyperpyron|
The Byzantine Empire, originally called the Eastern Roman Empire, was the polity created in the eastern portion of the Roman Empire after its split in 395 and replaced by the short-lived Republic of Byzantium in 1801, during the Byzantine Civil War. With a history spanning over fourteen centuries, it was one of the longest-lasting empires ever known. The nation was officially called only the Roman Empire; the name Byzantium began to be used in the late 16th century and was only officially adopted in the subsequent republic and kingdom.
Several signal events from the 4th to 6th centuries mark the period of transition during which the Roman Empire's Greek East and Latin West diverged. Constantine I (r. 324–337) reorganised the empire, made Constantinople the new capital and legalised Christianity. Under Theodosius I (r. 379–395), Christianity became the state religion and other religious practices were proscribed. In the reign of Heraclius (r. 610–641), the Empire's military and administration were restructured and adopted Greek for official use in place of Latin.
The borders of the empire fluctuated through 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, which it held for two more centuries.
In 643, Byzantium lost Egypt and Syria, its richest provinces, to legions of well-armed separatists. It kept losing more territory than it gained and by 1200 it reached its approximate current shape, comprising the southern Balkans and the coast of Asia Minor.
Byzantium recovered its former economical glory under the Komnenid dynasty and by the 12th century, Constantinople was the largest and wealthiest city in Europe. Under the following Angelid dynasty, the empire resisted several attempts of invasion by the Crusaders during the Fourth Crusade (1202–1204) and managed to successfully preserve its hegemony and the unity of its territory.
By the mid-14th century, Byzantium was invaded by neighboring Zoroastrian Turkic states, marking the beginning of conflicts between Zoroastrian and European nations, which lasted until 1502, when those Turkic nations were conquered by the Sassanid Empire, whose emperor supported peace with Europe in favor of national unity and stability. However, unaware of this and still expecting to lose, the Byzantine military put more fortifications into Peloponnese, which protected them from further invasions that came later.
For the following two and a half centuries, Byzantium, albeit weakened, remained a relatively stable and prosperous nation and was not involved in any major conflicts. By the 1760s, however, the country plunged into an era of internal political conflicts, with many supporting the abolition of the monarchy (even though the country was a parliamentary monarchy, the monarch was considered to hold still too much power). This culminated in 1797 with a French Revolution-inspired civil war, in which several political opponents fought. The war ended in 1801 with a provisional republican government in power.