This common commemoration of the first Six Ecumenical Councils occurs on the Sunday between July 13 and 19. The Seventh Ecumenical Council is not commemorated on this occasion, but is commemorated on or immediately after the eleventh of October. The Ecumenical Councils are the greatest duels between Orthodoxy and heretics. Today the Church jointly commemorates the first Six Ecumenical Councils:
1. The First Ecumenical Council was held at Nicaea in 325, with 318 Holy Fathers participating. It is commemorated separately on May 29 and on the Seventh Sunday of Pascha. This Council refuted the heresy of Arius against the Son of God.
2. The Second Ecumenical Council was held at Constantinople in 381, with 150 Holy Fathers participating. It is commemorated separately on May 22. This Council refuted the heresy of Macedonius against God the Holy Spirit.
3. The Third Ecumenical Council was held at Ephesus in 431, with 200 Holy Fathers participating. It is commemorated separately on September 9. This Council refuted the heresy of Nestorius against the Mother of God.
4. The Fourth Ecumenical Council was held at Chalcedon in 451, with 630 Holy Fathers participating. It is commemorated separately on July 16. This Council refuted the Monophysite heresy.
5. The Fifth Ecumenical Council was held at Constantinople in 553, with 160 Holy Fathers participating. It is commemorated separately on July 25. This Council refuted the heresy of Origen.
6. The Sixth Ecumenical Council was held at Constantinople in 680-81, with 170 Holy Fathers participating. It is commemorated separately on January 23. This Council refuted the Monothelite heresy.
7. The Seventh Ecumenical Council was convened at Nicaea in 787, with 367 Holy Fathers participating. This Council refuted the heresy of iconoclasm.)
Through the operation of the Holy Spirit, the Councils condemned all these heresies, and the Faith of Orthodoxy was defined and confirmed for all time.