At the second session of the [[Robber Council of Ephesus]] on [[August 22]], 449, Ibas, who was in prison in Antioch and was not called to defend himself<ref>Labbe, iv. 626, 634</ref>, was deposed.
After the Robber Council Pope [[Leo the Great |Leo I]] of Rome approached [[
Pulcheris the Empress|Pulcheria]], emperor Theodosius' sister for help in reversing the council's decisions. After the emperor's death in July 450 and Pulcheria's marriage to Marcian, the new emperor, Marcian, summons a general council that convened under Patr. Anatolius at [[Chalcedon]] in 451. At the council, the status of the bishops deposed by the Robber council was considered. The council, after much discussion restored Ibas unanimously on the condition that he anathematize Nestorius and Eutyches and accept the tome of Leo. Ibas consented without hesitation. He was restored as bishop of Edessa. Nonnus, who had been chosen bishop on Ibas' deposition, having been legitimately ordained, was allowed to retain his episcopal rank, and on Ibas's death, [[October 28]], 457, succeeded him as metropolitan <ref>Labbe, iv. 891, 917</ref>