Meaning : The largest city and former capital of Turkey. Rebuilt on the site of ancient Byzantium by Constantine I in the fourth century. Renamed Constantinople by Constantine who made it the capital of the Byzantine Empire. Now the seat of the Eastern Orthodox Church.

Meaning : The council in 869 that condemned Photius who had become the patriarch of Constantinople without approval from the Vatican, thereby precipitating the schism between the eastern and western churches.

Meaning : The sixth ecumenical council in 680-681 which condemned Monothelitism by defining two wills in Christ, divine and human.

Meaning : The fifth ecumenical council in 553 which held Origen's writings to be heretic.

Meaning : The second ecumenical council in 381 which added wording about the Holy Spirit to the Nicene Creed.