Held in 325, the First Council of Nicaea was the earliest worldwide ("ecumenical") council for the Christian Church. It was called by Emperor Constantine to achieve unity, in part by responding to the growing controversy of Arianism. It was held in Nicaea, Asia Minor (now İznik, Turkey).
Constantine - 306-337AD. ClickView video, 50min.
Constantine changed the course of world history by making Christianity the official state religion of Rome. He ruled for more than 30 years during which he ended the persecution of Christians and built countless churches.