Held in Chalcedon, near Constantinople, 451. Under Emperor Marcian. 630 Bishops were present.
Monophysite Controversy
The Council was concerned, once again, with the nature of Jesus Christ. The teaching arose that Christ's human nature (less perfect) dissolved itself in His divine nature (more perfect): like a cube of sugar in a post of water. Thus, in reality, Christ had only one nature, the Divine. Hence, the term: Monophysites ("mono", one and "physis", "nature".) Monophysitism overemphasized the divine nature of Christ, at the expense of the human.
Proclamation
The Council condemned Monophysitism and proclaimed that Christ has two complete natures: the divine and the human, as defined by previous Councils. These two natures function without confusion, are not divided nor separate (against Nestorius), and at no time did they undergo any change (against Eutyches: Monophysites).
Read about the other Ecumenical Councils: