constantinople

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

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

the sixth ecumenical council in 680-681 which condemned Monothelitism by defining two wills in Christ, divine and human

the fifth ecumenical council in 553 which held Origen's writings to be heretic

the second ecumenical council in 381 which added wording about the Holy Spirit to the Nicene Creed