Faced with theological and other major issues that it was clear would inpact the faith of the universal Christian Church, the ancient churches called Seven ecumenical (or œcumenical) to resolve them and to hold their conclusions as binding on all. All these were summoned by eastern emperors of the Roman Empire and largely controlled by Greek patriarchs and bishops. The decisions made at these councils were supposed—in theory, at least—to represent the collective mind of the Church (hence, the adjuective) and, therefore, binding on all Christians. They are:
1. The Council of Nicea (or Nicæa), 325, called by Constantine.
2. The First Council of Constantinople, 381, called by Theodosius.
3. The Council of Ephesus, 431, called by Theodosius II.
4. The Council of Calcedon, 451, called by Marcian and Pope Leo I.
5. The Second Council of Constantinople, 553, called by Justinian I.
6. The Third Council of Constantinople, 680, called by Constantine Pogonatus.
7. The Second Council of Nicea, 787, called by Irene and her son Constantine.
Of these the first four were of particular significance in establishing the orthodox formulation on the Trinity and the Incarnation.
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