Theodosius II, or Theodosios (Θεοδόσιος) was a Byzantine and Eastern Roman emperor of the 5th century. He promulgated the Codex Theodosianus and commissioned the construction of the Theodosian Walls. He was forced to manage conflicts with the Sassanid Persians, Huns, and Vandals. He most famously oversaw the Council of Ephesos which established the Orthodox Christological understanding of the Theotokos and condemned Nestorianism as heretical.