The 21 Councils, and the Crises Each One Faced

A quick-reference guide to every ecumenical council in the Church's history — and the specific error, schism, or corruption each one was called to confront.

It's easy to think of Church councils as distant, abstract events. In reality, every single one was summoned because something was genuinely at stake — a heresy spreading through whole regions, a corrupt election, a schism dividing the faithful, a reformer's challenge the Church needed to answer clearly. Below is each of the twenty-one ecumenical councils, paired with the crisis it was called to resolve.

1. First Council of Nicaea (325) — Arianism, which denied the full divinity of Christ.
2. First Council of Constantinople (381) — The lingering influence of Arianism; affirmed the full divinity of the Holy Spirit.
3. Council of Ephesus (431) — Nestorianism, which denied that Mary could rightly be called the Mother of God.
4. Council of Chalcedon (451) — Monophysitism, a confusion over how Christ's divine and human natures are united.
5. Second Council of Constantinople (553) — Christological disputes that continued to simmer after Chalcedon.
6. Third Council of Constantinople (680–681) — Monothelitism, the denial that Christ possessed a true human will.
7. Second Council of Nicaea (787) — Iconoclasm, the destruction of sacred images and icons.
8. Fourth Council of Constantinople (869–870) — The Photian schism, caused by an unlawful claim to the Patriarchate of Constantinople.
9. First Lateran Council (1123) — The Investiture Controversy, over whether secular rulers could appoint bishops.
10. Second Lateran Council (1139) — A papal schism caused by a rival antipope.
11. Third Lateran Council (1179) — Disputed papal elections and the rise of the Cathar heresy.
12. Fourth Lateran Council (1215) — Widespread doctrinal confusion; formally defined transubstantiation and mandated annual Confession and Easter Communion.
13. First Council of Lyons (1245) — Open conflict between Pope Innocent IV and Emperor Frederick II.
14. Second Council of Lyons (1274) — An attempt to heal the Great Schism between East and West.
15. Council of Vienne (1311–1312) — Corruption within the Knights Templar and the broader need for clerical reform.
16. Council of Constance (1414–1418) — The Western Schism, when three rival claimants each claimed to be the true pope.
17. Council of Basel–Ferrara–Florence (1431–1445) — Conciliarism, a movement challenging papal supremacy, alongside a further attempt at East-West reunion.
18. Fifth Lateran Council (1512–1517) — Deep-rooted Church corruption, addressed on the very eve of the Protestant Reformation.
19. Council of Trent (1545–1563) — The Protestant Reformation itself, and the doctrinal and disciplinary reform it demanded of the Church.
20. First Vatican Council (1869–1870) — The rise of rationalism and growing challenges to the authority of the papacy in the modern era.
21. Second Vatican Council (1962–1965) — The Church's pastoral relationship to the modern world, calling for renewal across liturgy, doctrine, and Church life.

A Pattern Worth Remembering

Looking at this list end to end, a pattern emerges that's worth sitting with: the Church has never once faced a crisis — heresy, corruption, schism, confusion — without eventually gathering her bishops, deliberating carefully, and speaking with clarity under the confirmation of the Chair of Peter. Some of these crises took decades to resolve. Some outlasted the popes who first confronted them. But none went unanswered forever.

For a family living through an unsettled moment in the Church's own life today, that's not a small thing to hold onto.