First ecumenical council

First Council of Nicaea
16th-century fresco depicting the Council of Nicaea
Date	20 May to 19 June, AD 325
Accepted by	Assyrian Church of the East Eastern Orthodox Oriental Orthodox Roman Catholicism
Next council	First Council of Constantinople
Convoked by	Emperor Constantine I
President	Hosius of Corduba (and Emperor Constantine)
Attendance	318 (traditional number) 250–318 (estimates) — only five from Western Church
Topics	Arianism, the nature of Christ, celebration of Passover (Easter), ordination of eunuchs, prohibition of kneeling on Sundays and from Easter to Pentecost, validity of baptism by heretics, lapsed Christians, sundry other matters.
Documents and statements	Original Nicene Creed, 20 canons, and a synodal epistle
Chronological list of Ecumenical councils

The First Council of Nicaea (/naɪˈsiːə/; Greek: Νίκαια [ˈni:kaɪja]) was a council of Christian bishops convened in the Bithynian city of Nicaea (now Iznik, Bursa province, Turkey) by the Roman Emperor Constantine I in AD 325. This first ecumenical council was the first effort to attain consensus in the Church through an assembly representing all of Christendom, although previous councils, including the first Church council, the Council of Jerusalem, had met before to settle matters of dispute. It was presided over by Hosius, bishop of Corduba who was in communion with the See of Rome.

Its main accomplishments were settlement of the Christological issue of the nature of the Son of God and his relationship to God the Father, the construction of the first part of the Nicene Creed, establishing uniform observance of the date of Easter, and promulgation of early canon law.