A Synopsis of the Seven Ecumenical Councils

1. Council of Nicaea (325) lasted two months and twelve days. Three hundred and eighteen bishops were present. Hosius, Bishop of Cordova, assisted as legate of Pope Sylvester. The Emperor Constantine was also present. To this council we owe The Creed (Symbolum) Of Nicaea, defining against Arius the true Divinity of the Son of God (homoousios), and the fixing of the date for keeping Easter (against the Quartodecimans).

2. First Council of Constantinople (381), under Pope Damasus and the Emperor Theodosius I, was attended by 150 bishops. It was directed against the followers of Macedonius, who impugned the Divinity of the Holy Ghost. To the above-mentioned Nicene creed it added the clauses referring to the Holy Ghost (qui simul adoratur) and all that follows to the end.

3. Council of Ephesus (431), of more than 200 bishops, presided over by St. Cyril of Alexandria representing Pope Celestine l, defined the true personal unity of Christ, declared Mary the Mother of God (theotokos) against Nestorius, Bishop of Constantinople, and renewed the condemnation of Pelagius.

4. Council of Chalcedon (451) -- 150 bishops under Pope Leo the Great and the Emperor Marcian defined the two natures (Divine and human) in Christ against Eutyches, who was excommunicated.

5. Second Council of Constantinople (553), of 165 bishops under Pope Vigilius and Emperor Justinian I, condemned the errors of Origen and certain writings (The Three Chapters) of Theodoret, of Theodore, Bishop of Mopsuestia and of Ibas, Bishop of Edessa; it further confirmed the first four general councils, especially that of Chalcedon whose authority was contested by some heretics.

6. Third Council of Constantinople (680-681), under Pope Agatho and the Emperor Constantine Pogonatus, was attended by the Patriarchs of Constantinople and of Antioch, 174 bishops, and the emperor. It put an end to Monothelism by defining two wills in Christ, the Divine and the human, as two distinct principles of operation. It anathematized Sergius, Pyrrhus, Paul, Macarius, and all their followers.

7. Second Council of Nicaea (787) was convoked by Emperor Constantine VI and his mother Irene, under Pope Adrian I, and was presided over by the legates of Pope Adrian; it regulated the veneration of holy images. Between 300 and 367 bishops assisted.

Not considered an Ecumenical Council by the Orthodox Church, but accepted by the Roman Church:

8. Fourth Council of Constantinople (869), under Pope Adrian II and Emperor Basil numbering 102 bishops, 3 papal legates, and 4 patriarchs, consigned to the flames the Acts of an irregular council (conciliabulum) brought together by Photius against Pope Nicholas and Ignatius the legitimate Patriarch of Constantinople; it condemned Photius who had unlawfully seized the patriarchal dignity. The Photian Schism, however, triumphed in the Greek Church, and no other general council took place in the East.