Bible & Christianity › Early church & the councils
Council of Nicaea
May–July 325· Council, creed or writing· Church, doctrine & the world
Historical recordConfirmed by archaeology, outside sources or contemporary records.
The first empire-wide church council, held in 325, which declared the Son fully divine and condemned Arius.
See it on the Bible & Christianity map →What it is
Constantine summoned bishops to Nicaea (İznik, Turkey), paying their travel. About 250–300 came, mostly from the East; tradition says 318. Rome's bishop sent two priests. The council condemned Arius, adopted a creed calling the Son 'of one being' (homoousios) with the Father, set a common way of dating Easter, and issued 20 rules (canons) on church order. Only two bishops refused to sign. In 2025 Pope Leo XIV and Patriarch Bartholomew marked its 1,700th anniversary at İznik.
Why it matters
It set the model of settling disputes by ecumenical (empire-wide) councils and produced the core of the creed most Christians still recite.
Think of it like
Like a major investor calling all the partners into one room to settle a dispute splitting the firm, and leaving with a signed agreement.
Sources and history
No full minutes survive. We have the creed, the canons, a letter from the council and eyewitness accounts by Eusebius of Caesarea and Athanasius.
Questions and debates
A popular myth says Nicaea chose the books of the Bible; it did not. How much Constantine steered its theology is still debated.
Inside this (5)
Connections (4)
▸Constantine the Great called Council of NicaeaHistorical record
The connection
Becoming sole emperor in 324, Constantine found the eastern church split over Arius. He sent Bishop Hosius of Córdoba to mediate, then summoned bishops to Nicaea, near his palace, at state expense. He opened the council in person, reportedly backed the word homoousios, and exiled those who refused to sign, setting the pattern of emperors calling councils.
When and where
Nicaea in Bithynia (İznik, Turkey), May–July 325; the meeting was first planned for Ancyra (Ankara).
Historical evidence
Eusebius of Caesarea, an eyewitness, describes it in his Life of Constantine and in a letter to his home church; several of Constantine's letters survive.
Questions and debates
Whether Constantine cared about theology or only unity is debated; he later recalled Arius and was baptized by an Arian-leaning bishop.
▸Council of Nicaea produced The Nicene CreedHistorical record
The connection
The bishops adopted a creed, possibly based on an existing local one, and inserted words aimed squarely at Arius: 'begotten, not made', 'of one being (homoousios) with the Father'. They added curses on anyone saying 'there was when he was not'. All but two bishops signed.
When and where
Nicaea, summer 325; the creed's adoption is traditionally dated June 19, 325.
Historical evidence
The creed's text survives in Eusebius's letter to his church at Caesarea, in Athanasius's writings and in the minutes of Chalcedon (451).
Questions and debates
Which existing creed served as the base, and who first proposed homoousios (perhaps Constantine, perhaps Hosius), are debated.
▸Council of Nicaea condemned Arius and the Arian controversyHistorical record
The connection
The council condemned Arius's teaching. Arius and two Libyan bishops who refused to sign were exiled to Illyricum (the Balkans), and Constantine ordered Arius's books burned. Yet within a few years Constantine let him return, and the dispute dragged on for more than half a century, until 381.
When and where
Nicaea, 325; exile to Illyricum; Arius was recalled around 327–328.
Historical evidence
The council's letter to the Egyptian churches, Constantine's letter ordering Arius's writings burned, and Socrates Scholasticus's Church History (c. 440).
Questions and debates
Arius's own views are known mostly from hostile quotations; whether most bishops signed from conviction or under imperial pressure is debated.
▸Pope Leo XIV marked the 1,700th anniversary of Council of NicaeaHistorical record
The connection
In 2025, 1,700 years after the council that wrote the first form of the Nicene Creed, Leo XIV made his first foreign trip to Turkey. At İznik, ancient Nicaea, he and Ecumenical Patriarch Bartholomew led an ecumenical prayer beside the ruins of an early basilica, professing the creed shared by Catholics, Orthodox and most Protestants.
When and where
İznik, Turkey, November 28, 2025; preceded by his apostolic letter on Nicaea, In unitate fidei (November 23, 2025).
Historical evidence
Vatican and Ecumenical Patriarchate records, news coverage and video of the service.
Questions and debates
Nicaea also set rules for dating Easter; whether East and West will agree on a common Easter date, as both leaders hope, remains open.