Theodosius II (AD 401 - 450) was emperor of the eastern Roman empire from 408 until his death in 450. He is most famous for having advanced the Theodosian Law Code, and for building the Theodosian walls of Constantinople.
He also presided over important Christological disputes, namely the First Council of Ephesus (AD 431) in which Nestorianism was declared heresy, and Theodosius had the Patriarch Nestorius deposed and exiled.
Theodosius also launched a campaign in 439 to reclaim the province of Africa when it was conquered by the Vandals, but this attempt failed. This military failure revealed the weakness of the Romans had reached at this point, and encouraged attacks on the Byzantines from both the Sassanians and the Huns.
Theodosius died in 450 as the result of a riding accident, and was succeeded by his sister Pulcheria, who married Marcian, making him the new emperor.