Eastern Roman (Civ5)/Civilopedia

In 293 AD Emperor Diocletian created a new administrative system for the unwieldy Roman Empire. He created a co-Augustus, selecting Maximian to oversee the eastern portion. Upon the abdication of Diocletian and Maximian, Constantine I formally divided the Roman holdings, and in 330 AD founded Constantinople as a "second Rome." So firmly established was the principle of two Romes that Theodosius I, upon his death in 395, bequeathed imperial rule to both his sons, Arcadius in the East and Honorius in the West. Theodosius the Great was the last to rule over an undivided empire.
Eastern Rome, often termed the Byzantine Empire, encompassed the southern Balkans, all of Anatolia and Egypt, and much of the Levant. It was spared much of the upheaval and warfare that plagued Western Rome in the 3rd and 4th centuries AD, due in large part to a succession of able emperors, a more established urban culture, and greater financial resources. The latter allowed the Byzantine emperors to placate barbarian invaders with tribute and hire mercenaries in large numbers.
The riches and skills brought by extensive trade permitted Theodosius II to extend and further fortify the walls of Constantinople during the first decades of the 400s, making the city virtually impervious (the walls were not breached until 1204 AD). Byzantine wealth also allowed Theodosius to buy off Attila, deflecting him to the west. Theodosius's successor Marcian refused to pay the exorbitant annual tribute and the Hunnic Empire soon collapsed with Attila's death in 453. Indeed, many of the surviving Huns would serve as mercenaries in Eastern Rome's subsequent wars with the Sassanids and Arabs.
After the death of Attila, the eastern empire enjoyed a long period of peace and internal stability, while the western empire collapsed in invasion and chaos. The end of Rome in the west is generally dated in 476 AD when Odoacer deposed Romulus Augustus. The Byzantine Emperor Zeno hired the Ostrogoths under their king Theodoric to reclaim the west. Theodoric led his forces into Italy and deposed Odoacer, establishing his own Kingdom of Italy. By urging the Ostrogoths to conquer Italy and Rome, and maintaining amiable relations with Theodoric, Zeno had both rid Eastern Rome of an unruly threat and gained nominal supremacy over Western Rome.