“City (Year) Decision”.

1. Nicea (325)

Rejected Arianism (the Son of God was the first creation of God the Father) and affirmed that the Son of God is of the same essence (homoousion) as the Father. Wrote the Nicene Creed.

2. Constantinople (381) 

Rejected the teachings of the Macedonians, who denied the deity of the Holy Spirit. Expanded the Nicene Creed.

3. Ephesus (431)

Christ was affirmed to be one Person, with two full and complete natures against the views of Apollinarius (the “rational soul” of Jesus was replaced by the Logos) and Nestorius (who separated the two natures so that He was two persons).

4. Chalcedon (451)

Rejected the teachings of the Eutyches (who said the humanity of Jesus was absorbed by the deity of the Son) and wrote the Definition of Chalcedon, which declared that Jesus is consubstantial with His Father according to” His divine nature and consubstantial with us according to His human nature and that these two natures are not confused, changed, divided, or separated.

5. Constantinople (553)

Affirmed the first four councils, especially Chalcedon, which was being attacked by heretics.

6. Constantinople (680–81) 
Condemned monothelism (belief which said Christ had only one will) and affirmed that Christ had two wills, a divine and a human will which worked in harmony.

7. Nicea (787)
Declared that the reverencing of icons of Christ and the saints was legitimate.1

1. The declaration of this Council is one that Reformed churches reject as violating the Second Commandment (e.g., Heidelberg Catechism, Q&A 96; Westminster Larger Catechism, Q&A 109). For more on the subject of images of Jesus Christ, see Daniel R. Hyde, In Living Color: Pastoral Counsel on Images of Jesus (Grandville, MI: Reformed Fellowship, 2008).”

Source: God With Us: Knowing the Mystery of Who Jesus Is.Pg 84-85. by Daniel R. Hyde.