21 church councils

1.First Council of Nicaea 325

Defined Christ’s divinity; condemned Arianism

2.First Council of Constantinople 381

Affirmed Holy Spirit’s divinity

3.Council of Ephesus 431

Declared Mary "Mother of God"

4.Council of Chalcedon 451

Defined Christ’s dual nature

5.Second Council of Constantinople 553

Rejected Nestorianism; clarified Christology

6.Third Council of Constantinople 680

Rejected Monothelitism; affirmed two wills

7.Second Council of Nicaea 787

Restored veneration of icons

8.Fourth Council of Constantinople 869

Addressed Photian Schism; deposed Photius

9.First Lateran Council 1123

Confirmed clerical celibacy; Church independence

10.Second Lateran Council 1139

Invalidated simony and clerical marriage

11.Third Lateran Council 1179

Regulated papal elections; condemned Waldensians

12.Fourth Lateran Council 1215

Defined transubstantiation; launched crusades

13.First Council of Lyon 1245

Deposed Emperor Frederick II; addressed crusades

14.Second Council of Lyon 1274

Filioque; Attempted East-West reunification

15.Council of Vienne 1311

Suppressed Knights Templar; reformed Church

16.Council of Constance 1414

Ended Western Schism; against Hussites: receive one species

17.Council of Florence 1431

Filioque; attempted East-West unity

18.Fifth Lateran Council 1512

Addressed Church reform; condemned simony, concubinage

19.Council of Trent 1545

Counter-Reformation; clarified Catholic doctrine

20.First Vatican Council 1869

Defined papal infallibility; addressed modernism

21.Second Vatican Council 1962

Mass in vernacular; promoted ecumenism; emphasizes scripture & laity