Conflict with Eutyches
The defining struggle of Flavian's patriarchate concerned Eutyches, an influential archimandrite at Constantinople who taught that Christ's humanity was absorbed into his single divine nature. At the Home Synod of Constantinople on 8 November 448, over which Flavian presided with about forty bishops present, Eusebius of Dorylaeum laid charges against Eutyches, and the synod deposed him.
Eutyches appealed against the sentence and gained the support of Dioscorus of Alexandria. Emperor Theodosius II, by some accounts displeased with Flavian over his refusal to pay the customary gratuities to the powerful court eunuch Chrysaphius, convened a new council to reopen the matter.