First Council of Nicaea

On May 20, 325, the First Council of Nicaea was formally opened, starting the first ecumenical council of the Christian Church. The Council of Nicaea eventually settled the question on the divine nature of God the Son and his relationship to God the Father. It also established of the first part of the Nicene Creed, and it settled on a uniform method for calculating the yearly observance of Easter. The Eastern Orthodox Christian tradition maintained that the double procession of the Holy Spirit from both the Father and the Son was incompatible with Orthodox doctrine.