Theology · Church History and the Fathers

What Were the Ecumenical Councils, and Why Were They Called?

The Church in Council

When the early Church faced its first great dispute, over whether Gentile converts had to follow the Jewish law, the apostles and elders met in Jerusalem to decide. The Acts of the Apostles records their decision with a remarkable phrase: “it has seemed good to the Holy Spirit and to us” (Acts 15:28).

That Council of Jerusalem, around the year 49, set a pattern. When serious questions arise, the bishops of the Church gather to discern, under the guidance of the Spirit, what the faith requires.

What Makes a Council “Ecumenical”?

Many councils and synods have been held throughout history, at local, regional and national levels. An ecumenical council (from the Greek oikoumene, “the whole inhabited world”) is a gathering of the bishops of the whole Church.

The Catholic Church teaches that an ecumenical council exercises supreme authority over the universal Church. But a council is ecumenical only if it is convoked, or at least confirmed or accepted, by the successor of Peter (Lumen Gentium 22; CCC 884). When an ecumenical council solemnly defines a doctrine of faith or morals, its definition is infallible (CCC 891).

The Catholic Church recognises 21 ecumenical councils. The Orthodox Churches recognise the first seven.

The First Seven: Defining Christ

The first seven councils, held in the East between 325 and 787, are shared by Catholics and Orthodox. Most of them were called to settle questions about who Christ is.

1. Nicaea I (325). Called by the Emperor Constantine to answer Arius, a priest of Alexandria who taught that the Son was a creature, not eternal God. The council taught that the Son is homoousios, “of the same substance” as the Father. It produced the first form of the Nicene Creed. Catholics and Orthodox marked its 1,700th anniversary together in 2025.

2. Constantinople I (381). Confirmed Nicaea and affirmed the full divinity of the Holy Spirit, expanding the Creed into the form recited at Mass today.

3. Ephesus (431). Rejected the teaching associated with Nestorius, which seemed to divide Christ into two persons, and proclaimed Mary Theotokos, Mother of God.

4. Chalcedon (451). Taught that Christ is one Person in two natures, divine and human, “without confusion, without change, without division, without separation.” Pope St Leo the Great’s letter, the Tome, was greeted with the cry, “Peter has spoken through Leo!” (See What Is the Hypostatic Union?)

5. Constantinople II (553). Clarified Chalcedon’s teaching against misinterpretations.

6. Constantinople III (680–681). Taught that Christ has two wills, divine and human, the human will freely obedient to the divine.

7. Nicaea II (787). Defended the veneration of icons against the iconoclasts, who wanted to destroy sacred images. It distinguished worship (latria), due to God alone, from veneration, which may be given to images and saints.

The Medieval Councils

After the split between East and West in the eleventh century, the councils were held in the West.

Lateran IV (1215), under Pope Innocent III, is the most important of these. It used the word transubstantiation for the change of bread and wine into Christ’s Body and Blood, and required Catholics to confess and receive Communion at least once a year.

Lyons II (1274) and Florence (1438–1445) sought reunion with the Orthodox. Florence achieved a formal union, including agreement on the filioque and purgatory, but it was rejected in the East and did not last. (See What Is the Filioque?)

Constance (1414–1418) ended the Western Schism, when two and then three men claimed to be pope at the same time.

Trent: The Response to the Reformation

The Council of Trent (1545–1563) met in three periods over eighteen years. It responded to the Protestant Reformation by defining Catholic teaching on Scripture and Tradition, the canon of the Bible, original sin, justification, the seven sacraments, the Mass as sacrifice, purgatory and more. It also launched major reforms, including the establishment of seminaries to train priests. Its decrees shaped Catholic life for four hundred years.

The Vatican Councils

Vatican I (1869–1870) taught on faith and reason in Dei Filius, and defined the primacy and infallibility of the Pope in Pastor Aeternus. It was cut short when Italian troops captured Rome.

Vatican II (1962–1965), called by Pope St John XXIII, was the largest council in history, with over 2,000 bishops. It issued sixteen documents, including four constitutions: on the liturgy (Sacrosanctum Concilium), on the Church (Lumen Gentium), on revelation (Dei Verbum), and on the Church in the modern world (Gaudium et Spes). It defined no new dogmas, but it taught with the full authority of an ecumenical council on a wide range of questions. Its interpretation has been widely debated ever since.

How Councils Teach

Not every word of a council carries the same weight. Councils have issued:

dogmatic definitions, often in the form of canons (“if anyone says… let him be anathema”), which are infallible;
doctrinal teaching, which Catholics accept with religious assent;
disciplinary decrees, which govern Church practice and can be changed by later authority.

For example, Trent’s definition that the Mass is a true sacrifice is a matter of faith. Its rules about the training of priests were disciplinary and have since been revised.

Why Councils Matter

The councils show the Church working as Christ intended: as a body, led by the successors of the apostles in union with Peter’s successor, guided by the Holy Spirit. They show how doctrine develops: usually not by inventing new teaching, but by defining the faith more precisely in response to error.

They also show that the Church does not change her mind on matters of faith. Each council builds on those before it. Vatican II cited Trent and Vatican I; Trent cited Nicaea. Seventeen centuries of councils form a single, continuous witness.