Third Council of Ephesus, (449), a controversial Christian council in Ephesus convened by the Eastern Roman emperor Theodosius II with Dioscorus, the patriarch of Alexandria, to uphold the monophysite Eutyches. The gathering was denounced by Pope Leo I as “the robber synod.”

Dioscorus was a miaphysite and thus held the Christological perspective that both the human and the divine natures of Jesus Christ are equally present in his person in one single nature through the mystery of the Incarnation. Dioscorus had originally sided with the Synod of Constantinople in 448 when it condemned the monk Eutyches for his theology. Eutyches espoused a form of monophysitism that emphasized the divine nature of Jesus at the expense of his human nature, a Christology that would later become known as the Eutychian heresy. Shortly after the Synod of Constantinople, however, Dioscorus became convinced that Eutyches had rejected his argument about Christ’s human nature and sought to reinstate the maligned monk.

The following year, with the support of Theodosius II, Dioscorus convened the Third Council of Ephesus. In a bold act, Dioscorus reinstated Eutyches and deposed Flavian, a champion of the doctrine of the two natures of Christ, as patriarch of Constantinople. Dioscorus concurred in the anathematization of Flavian and other bishops over the protests of the papal legate and even attempted to excommunicate Leo I for his condemnation of Eutyches.

The monophysite doctrine of the one nature of Christ was condemned in 451 during the Council of Chalcedon, and Dioscorus was deposed and excommunicated.