The Ecumenical Councils

The first ecumenical council was convened by Emperor Constantine to settle the controversy ignited by Arius, a presbyter of Alexandria, who taught that the Son of God was a created being — that 'there was when he was not.' Roughly 300 bishops gathered and rejected this teaching, confessing that the Son is 'begotten, not made, of one substance (homoousios) with the Father.' The council produced the original Nicene Creed, issued twenty canons on church order, and established a common method for calculating the date of Easter. Nicaea matters because it defined the full divinity of Christ as the church's non-negotiable faith and set the precedent of resolving doctrinal crises through ecumenical councils. The young deacon Athanasius, attending with his bishop Alexander, became the creed's lifelong defender.

Key figures: Constantine I, Alexander of Alexandria, Athanasius, Hosius of Cordova, Eusebius of Caesarea, Arius

In the decades after Nicaea, Arianism revived under imperial patronage, and a new dispute arose: the Pneumatomachians ('Spirit-fighters,' or Macedonians) denied the full divinity of the Holy Spirit, while Apollinaris taught that Christ lacked a human rational soul. Emperor Theodosius I summoned about 150 bishops to Constantinople, where the council reaffirmed Nicene faith and expanded the creed's third article, confessing the Holy Spirit as 'the Lord and Giver of Life, who proceeds from the Father, who with the Father and the Son together is worshipped and glorified.' It also condemned Apollinarianism. The resulting Niceno-Constantinopolitan Creed became, and remains, the most widely used confession of faith in Christendom, recited in the liturgies of East and West. Gregory of Nazianzus, the great Trinitarian theologian, briefly presided.

Key figures: Theodosius I, Gregory of Nazianzus, Meletius of Antioch, Gregory of Nyssa, Nectarius of Constantinople

Nestorius, archbishop of Constantinople, objected to calling the Virgin Mary Theotokos ('God-bearer'), preferring Christotokos — language his critics heard as splitting Christ into two persons, one divine and one human. Cyril of Alexandria led the opposition, insisting that the one person of the eternal Word truly took flesh and was born of Mary, so that her child is God the Son. The council, convened by Emperor Theodosius II, deposed Nestorius, upheld the title Theotokos, and endorsed Cyril's teaching that Christ is one person. It also condemned Pelagianism in the West and forbade composing any rival creed to that of Nicaea. Ephesus matters because it safeguarded the unity of Christ's person: the one who was crucified is the same one who is eternally God.

Key figures: Cyril of Alexandria, Nestorius, Theodosius II, Celestine I, Memnon of Ephesus

Reacting against Nestorianism, the Constantinopolitan archimandrite Eutyches taught that after the incarnation Christ had only one nature, his humanity absorbed into his divinity. A packed council at Ephesus in 449 vindicated him, but Pope Leo I denounced that gathering as a 'robber synod.' Emperor Marcian then convened over 500 bishops at Chalcedon, which deposed Dioscorus of Alexandria, rehabilitated those wrongly condemned, and — drawing on Leo's Tome and Cyril's letters — issued the Chalcedonian Definition: one and the same Christ, perfect in Godhead and perfect in manhood, acknowledged in two natures 'without confusion, without change, without division, without separation,' united in one person. Chalcedon remains the touchstone of orthodox Christology for the Eastern Orthodox, Roman Catholic, and Protestant traditions, though the non-Chalcedonian Oriental Orthodox churches rejected it.

Key figures: Leo I (the Great), Marcian, Pulcheria, Flavian of Constantinople, Eutyches, Dioscorus of Alexandria

A century after Chalcedon, large parts of Egypt and Syria still rejected the council as crypto-Nestorian. Emperor Justinian I, seeking to reconcile them, pressed for the condemnation of the 'Three Chapters' — the person and works of Theodore of Mopsuestia, certain writings of Theodoret of Cyrus against Cyril, and the letter of Ibas of Edessa — texts the anti-Chalcedonians regarded as tainted with Nestorianism. The council duly anathematized the Three Chapters and reaffirmed the christology of Cyril and the previous four councils, interpreting Chalcedon in a firmly anti-Nestorian sense; teachings associated with Origen were also condemned in this period. Pope Vigilius resisted before finally assenting. The council matters as the church's authoritative clarification that Chalcedon's 'two natures' never meant two persons: the one subject in Christ is God the Word.

Key figures: Justinian I, Eutychius of Constantinople, Vigilius

Held in 680–681, this council resolved the Monothelite controversy. In a bid to win back the non-Chalcedonians, seventh-century emperors and Patriarch Sergius of Constantinople had promoted the formula that Christ, though in two natures, possessed only one will and one energy. Maximus the Confessor argued that this quietly undid Chalcedon: a human nature without a human will is not a real humanity, and Christ's obedience in Gethsemane — 'not my will, but thine' — requires a genuine human will freely conformed to the divine. Backed by Pope Agatho's letter, the council under Constantine IV defined that Christ has two natural wills and two natural energies, without division or confusion, the human will following and subject to his divine will. It anathematized the Monothelite leaders, including Sergius and Pope Honorius I.

Key figures: Constantine IV, Agatho, Maximus the Confessor, Sergius of Constantinople, Honorius I

From 726 the Byzantine emperors Leo III and Constantine V waged a campaign against the veneration of icons, destroying images and persecuting their defenders; the iconoclast council of Hieria (754) declared icons idolatrous. Theologians such as John of Damascus replied that because the invisible God had truly become visible flesh in Jesus Christ, he could be depicted, and that honor shown to an image passes to the one portrayed. Under the empress Irene, with Patriarch Tarasius presiding, the council restored the icons, distinguishing the veneration (proskynesis) properly given to images and saints from the worship (latreia) due to God alone. The last council recognized as ecumenical by both East and West, Nicaea II grounded Christian art in the doctrine of the incarnation; its triumph is still celebrated in Orthodoxy as the 'Triumph of Orthodoxy.'

Key figures: Irene of Athens, Tarasius of Constantinople, John of Damascus, Hadrian I