Following the death of Theodosius II on July 28, AD 450, an undistinguished military officer of provincial origin, Marcian, was elevated to the eastern imperial throne.The circumstances surrounding Theodosius’ accidental death and Marcian’s unexpected rise to power have received less scholarly attention than they deserve, given their concurrence with the climax of the most divisive theological conflict of the fifth century, the miaphysite/dyophysite Christological controversy. Marcian’s elevation and his subsequent reversal of Theodosius’ theological policy sparked a violent church schism that continued to plague the empire under Justinian in the sixth century, and whose repercussions are still felt in the Catholic and Orthodox churches today. Those scholars who have treated the events of 450 in detail have significantly advanced our understanding of the circumstances surrounding Marcian’s accession, but they have tended to oversimplify the socio-political forces at play. This paper is primarily a summary and analysis of the extant prosopographical data made with a view towards reconstructing a fuller picture of the military and theological/ecclesiastical factions that made up the court political scene in the final years of Theodosius’ reign and in the ensuing interregnum. Following the analysis, I will put forward my own theory, that the choice of Marcian as emperor represented a careful compromise between disgraced military factions seeking a return to imperial favor, the dyophysite partisans brought to grief at the Second Council of Ephesus, and the emperor’s sister, Pulcheria, anxious to return to the imperial palace from which she had been exiled years before.