The First Ecumenical Council: [[Council of Nicaea|First Council of Nicaea]] 325, called by the Roman Emperor [[Constantine]] the Great with Pope [[Saint Sylvester I]] sitting on the Throne of Peter as the 33rd successor of Saint Peter.
The Second Ecumenical Council: [[Constantinople I|First Council of Constantinople]] 381 convened by the Roman Emperor of the East [[Theodosius I]]. Neither the Holy Father Pope Saint [[Damasus I]] or his papal legates attended because of friction between him and the emperor over authority. Already the split between East and West was manifesting itself. 186 bishops did attend, including [[Saint Gregory Nazianzen]] and Saint [[Cyril of Jerusalem]]. Canon 3 of this Council states: "''Because it is new Rome, the bishop of Constantinople is to enjoy the privileges of honor after the bishop of Rome.''"<ref>[http://papalencyclicals.net/Councils/ecum02.htm#3 Canon iii]</ref>
The Third Ecumenical Council: [[Council of Ephesus]] 431 called by the Roman Emperor of the East Theodosius II, influenced by his saintly sister [[Saint Pulcheria]], in harmony with Pope [[Saint Celestine I]].