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The second ecumenical council in 381 which added wording about the Holy Spirit to the Nicene Creed
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The fifth ecumenical council in 553 which held Origen's writings to be heretic
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The sixth ecumenical council in 680-681 which condemned Monothelitism by defining two wills in Christ, divine and human
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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
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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