Nicaea, Council Of

(325), the first ecumenical council of the Christian church, meeting in ancient Nicaea (now Iznik, Tur.). It was called by the emperor Constantine I, an unbaptized catechumen, or neophyte, who presided over the opening session and took part in the discussions. He hoped a general council of the church would solve the problem created in the Eastern church by Arianism, a heresy first