Theodosius II was Roman emperor from 402 to 450. He was proclaimed augustus as an infant and ruled as the Eastern Empire's sole emperor after the death of his father, Arcadius, in 408. His reign was marked by the promulgation of the Theodosian law code and the construction of the Theodosian Walls of Constantinople. He also presided over the outbreak of two great Christological controversies, Nestorianism and Eutychianism.

The Byzantine Empire, also referred to as the Eastern Roman Empire, was the continuation of the Roman Empire centered in Constantinople during Late Antiquity and the Middle Ages. The eastern half of the Empire survived the conditions that caused the fall of the West in the 5th century AD, and continued to exist until the fall of Constantinople to the Ottoman Empire in 1453. During most of its existence, the empire remained the most powerful economic, cultural, and military force in the Mediterranean world. The term "Byzantine Empire" was only coined following the empire's demise; its citizens referred to the polity as the "Roman Empire" and to themselves as "Romans". Due to the imperial seat's move from Rome to Byzantium, the adoption of state Christianity, and the predominance of Greek instead of Latin, modern historians continue to make a distinction between the earlier Roman Empire and the later Byzantine Empire.