You have probably heard this one, in a novel or a documentary or at a bar. In 325, Emperor Constantine gathered the bishops at Nicaea, and they voted on which books would be in the Bible.
It did not happen. The record has no hint of it.
What happened at Nicaea
About 250 to 300 bishops met in the summer of 325. Their main problem was Arius, a priest in Alexandria who taught that the Son was created, and so was not fully God. The council rejected him and issued a creed. They also fixed a method for dating Easter and passed about twenty rules on matters like clergy discipline.
We have the creed and those canons. We also have accounts from people who were present, including Eusebius and Athanasius. Neither mentions a discussion of which books belonged in scripture. Nobody writing at the time thought that had happened.
Where the myth comes from
The earliest source seems to be a much later Greek document, the Synodicon Vetus, from around the ninth century. It tells a story in which the books were placed on an altar and the false ones fell to the floor. Voltaire repeated it to mock the church, and in 2003 The Da Vinci Code gave it its modern form.
What really happened
Slowly, through use. Look at the canon log for the whole story, but the short version goes like this.
The four gospels and Paul’s letters were in wide use by about 200, when Irenaeus was already arguing there could be only four. Books such as James, Jude and Revelation remained disputed for much longer. Eusebius, around the time of Nicaea, sorts the books into accepted and disputed, which he could not have done if a council had just decided.
In 367, Athanasius listed exactly our 27. Regional councils in North Africa approved the list in the 390s. Even then, a Bible of that era might carry extra books, and the Syriac churches went on with a shorter list for a long time.
The Old Testament took longer still. Catholics formally defined their list at Trent in 1546, a response to Luther moving the books. Protestants did not settle in practice until a Bible society’s funding decision in 1826. Ethiopia never did agree with any of them.
Why this matters
The Nicaea story is attractive because it gives you a villain and a date. It makes the canon something a few powerful men did in a room, which means it can be undone by exposing them.
The true story is harder to dismiss, and harder to revere. Thousands of communities, over centuries, kept reading some books and stopped reading others, under pressure from bishops, with real losers. It is not a conspiracy. It is closer to an edit, made slowly, by a great many hands.
Common questions
Did Constantine decide what went in the Bible?
No. Constantine called the Council of Nicaea in 325 and later ordered 50 Bibles from Eusebius, but no record shows him choosing the books. Most of the canon had been in use long before him, and arguments about the rest continued long after.
Who decided which books went in the Bible?
No single body did. The New Testament emerged through use in churches over about three centuries. Athanasius listed the 27 books in 367, regional synods endorsed them in the 390s, and the Catholic Church formally defined its full list only at Trent in 1546.
What was the Council of Nicaea about?
Mainly the Arian controversy, over whether the Son is fully divine. It also dealt with the date of Easter and rules for clergy, and it produced the original Nicene Creed.