The First Council of Nicaea (pronounced ny-SEE-uh; Greek: Sýnodos tês Nikaías) was a gathering of Christian bishops called by the Roman emperor Constantine I in Nicaea—a city in Bithynia (modern İznik, Turkey). It met from May through late July 325.
As the church’s first ecumenical council, it marked an early effort to build unity across Christianity by bringing together leaders from throughout the empire. Hosius of Corduba likely presided. With at least 200 bishops present, the council’s chief achievements were defining the Son’s relationship to the Father in response to controversy, drafting the opening portion of the Nicene Creed, establishing a common method for determining the date of Easter, and issuing early church canons (rules of discipline).
Background
The Alexandrian controversy (Arian dispute)
The council was largely prompted by a theological conflict in Alexandria over who Jesus is in relation to God the Father. Scholars commonly date the start of the dispute to sometime between 318 and 322. The main figures were Alexander, bishop of Alexandria, and Arius, a presbyter.
Alexander taught that the Son is eternally generated from the Father. Arius and his supporters argued instead that the Father alone is eternal and that the Son was brought into being by the Father—meaning the Son had a beginning and was therefore subordinate. Arius also accused Alexander of leaning toward Sabellianism, which treated Father, Son, and Spirit as one person rather than distinct.
A local synod of bishops from Egypt and Libya supported Alexander. Arius refused its ruling and was excommunicated and exiled from Alexandria. He then sought support across the eastern churches through letters and travel. Prominent supporters included Eusebius of Nicomedia and Eusebius of Caesarea, while Alexander circulated letters defending his position.
The Melitian schism
At the same time, the Alexandrian church faced a separate internal split led by Melitius of Lycopolis. During the persecutions, Melitius had taken on roles associated with Alexandria’s leadership; after 311 he refused to surrender ordination authority or recognize the authority of Alexander and earlier Alexandrian successors.
Constantine and the council’s convening
In 324, Constantine defeated Licinius and became sole ruler of the empire. Around this time, he learned of the Alexandrian dispute (possibly through Eusebius of Nicomedia) and wrote to Alexander and Arius urging reconciliation.
Constantine sent Hosius of Corduba to Alexandria. Hosius apparently became involved first in discussions about the date of Easter, and later in calling a larger meeting of eastern bishops at Antioch, which backed Alexander and issued a statement of faith rejecting Arius’s ideas. After these efforts failed to restore unity, Constantine called a broader council. Although an earlier meeting may have been planned for Ancyra, Constantine relocated it to Nicaea, close to his residence at Nicomedia, making attendance easier and allowing him to be present—also fitting with celebrations for the twentieth year of his reign.
Attendance and setting
The imperial treasury covered travel and expenses. Ancient reports vary, but the traditional figure became 318 bishops, though surviving signature lists suggest roughly 200–220. With assisting clergy (presbyters and deacons), total attendance may have reached 1,200–1,900.
Most bishops came from the eastern provinces, with smaller western representation (including Hosius and delegates associated with Rome). The council met in the imperial palace at Nicaea, likely in a basilica-style hall.
Overview of proceedings
Constantine opened the council with a formal entrance and delivered an introductory address in Latin. Hosius probably supervised the debates as Constantine’s representative. Constantine participated in discussion (in Greek) but did not vote as a bishop. Because no detailed official minutes survive, the exact sequence of debate is uncertain, though the council likely first resolved who could participate—such as bishops previously excommunicated at Antioch.
The bishops then debated a creed line by line, ultimately adopting a text that nearly all accepted. Alongside the Arian controversy, they addressed the Easter dating question, dealt with the Melitian schism, and issued twenty canons. The council concluded in early July, with bishops invited to Constantine’s twentieth-anniversary celebration on 25 July, and letters were circulated to announce the decisions.
Why it mattered as an ecumenical council
Nicaea is remembered as the first attempt to summon a council representing the whole church across the empire—what later writers called “ecumenical,” meaning “worldwide” in the sense of the inhabited world (largely the Roman world). It set a lasting model: major councils would define doctrine through creeds and regulate church life through canons, launching the era commonly counted as the first seven ecumenical councils.
The Nicene Creed (main outcome)
The council produced a creed that clearly defined the church’s faith and drew boundaries against Arian claims. It declared the Son to be:
-
“true God from true God”
-
“begotten, not made”
-
“of one substance with the Father” (homoousios)
It concluded with anathemas rejecting statements such as “there was when he was not” and affirming the Son’s unchangeability.
Later, the creed was expanded at the Council of Constantinople (381).
Other major decisions
-
Exile and enforcement: Arius and a small number of supporters refused to endorse the creed and were exiled; his writings were ordered destroyed.
-
Easter: The council endorsed a unified approach associated with Rome and Alexandria and separated Christian computation from dependence on the Jewish calendar.
-
Melitian schism: Melitius was restricted, his ordinations were regularized, and his group was subordinated to Alexandrian authority.
-
Canon law: Twenty canons established early disciplinary norms for clergy and church order.
If you want, I can rewrite this again in a shorter “textbook paragraph” style or in a more modern/plain-English tone.
.jpg)
.jpg)