What happened in 325 CE
The Council of Nicaea was a gathering of bishops convened by the Roman emperor Constantine in the city of Nicaea, in what is now İznik, Turkey. Ancient sources disagree on how many bishops attended, but the usual estimate is roughly three hundred, most of them from the eastern half of the empire.
Constantine had recently gained control of the whole empire, and a dispute among Christian leaders threatened the unity he wanted. The meeting was as much a matter of church leadership as of imperial politics, and that overlap is one reason the council still attracts so many competing stories.
The central dispute
The main question was how to describe the relationship between God the Father and the Son. A priest from Alexandria named Arius taught that the Son was created and therefore subordinate to the Father. His opponents, including Bishop Alexander of Alexandria and, later, Athanasius, argued that the Son shared the Father’s divine nature.
The council produced a statement of belief, the early form of what is now called the Nicene Creed, and condemned the position associated with Arius. The creed was revised at the Council of Constantinople in 381, so the version recited in many churches today is not word for word the text of 325.
Other business
Nicaea also addressed practical matters. The bishops sought a common approach to calculating the date of Easter, and they issued a set of disciplinary rulings, usually numbered as twenty canons, on subjects such as the conduct of clergy and the readmission of those who had left the church during persecution.
These topics are less dramatic than the myths, but they are what the surviving documents actually describe.
The claims that do not hold up
A widely repeated claim says the council voted on which books belong in the Bible. Historians do not find support for this in the records. The formation of the biblical canon was a gradual process that unfolded over centuries, and the surviving accounts of Nicaea do not describe a vote on a list of scriptures.
Another popular claim says the council invented the divinity of Jesus. The debate at Nicaea was about how to define a relationship that Christians were already discussing and disagreeing about. The sources show a dispute over interpretation, not the sudden creation of a new belief.
How to check a Nicaea claim yourself
When you meet a bold statement about the council, look for the earliest source that supports it. Eusebius of Caesarea, Athanasius and later church historians such as Socrates Scholasticus and Sozomen all wrote about the event, though each had a point of view. The creed and canons survive in the records of the council tradition.
If a retelling cannot point to any of these, treat it as a lead to investigate rather than a settled fact. Careful readers can hold two ideas at once: the council was shaped by politics and power, and it is also easy to attribute to it things the evidence does not show.