The Byzantine Empire, also known as Byzantium, is a large political unit that comprised the eastern region of what was once known as the Roman Empire. Thus, it is sometimes referred to as the Eastern Roman Empire, though historians did not use the aforementioned designations until long after the empire ceased to exist. The Byzantine Empire was named after its capital city, which became better known as Constantinople. Lasting for more than eight centuries, the Byzantine Empire was one of the largest and most powerful economic, political and military powers in the world.
As early as 285, Roman Emperor Diocletian appointed fellow military officer Maximian as co-emperor, and he appointed two more within the next decade. Constantine the Great, who was Roman Emperor from 306 to 337, is often credited for furthering the concept of the Byzantine Empire when he established Constantinople in 324. The city was situated east of Rome, which was the empire's capital. Thus, Constantinople became the eastern administrative seat of the empire, or a second Rome of sorts.
The founding of Constantinople set the stage for the eventual official partition of the Roman Empire. Upon his death in 395, Emperor Theodosius I divided the empire between his two sons. Arcadius was left in charge of the East, with Constantinople serving as its capital. Honorius, meanwhile, took over the West with the capital at Rome.
The West, now referred to as the Western Roman Empire, was on its last legs, though. Weakened largely by invading tribes and internal instability, it eventually fell in 476. Within a decade, however, the Byzantine Empire had managed to recapture the territories that had belonged to the vanquished Western Roman Empire. The most successful emperor in this enterprise was Justinian I, also known as Justinian the Great, who ruled from 527 to 565. The empire's subsequent control of the western Mediterranean area not only affirmed its strength, but made it wealthier as well.
By the reign of Heraclius, from 610 to 641, the Byzantine Empire was distinguishing its identity the defunct Western Roman Empire with the use of Greek instead of Latin as its official language. This lingual shift would be confirmed with the East-West Schism of 1054, when the Catholic Church was split into the Greek Orthodox Church, or the Eastern Orthodox Church, and the Western Latin branch, which became the Roman Catholic Church. The 7th century also marked the time that the empire began to shrink and rattle due to massive conflicts with groups such as the Arabs and Muslims. A certain measure of luster was restored with the Komnenos dynasty of 1081 to 1185, but a long succession of ineffective leaders, fragile governmental infrastructure and constant attacks on Constantinople were some of the fatal problems the empire faced during its last years. The capital city finally fell to the army of the Ottoman Empire in 1453, effectively bringing the Byzantine Empire to an end.