More than two years after it was published, "The Da Vinci Code" remains a huge best-seller-and a point of contention among evangelical Christians, most of whom consider it blasphemous. Still, "The Da Vinci" juggernaut moves forward. In the last couple of weeks, Sony Pictures, the studio behind the Ron Howard-directed adaptation of Dan Brown's novel, has released a short "Da Vinci Code" trailer, which is playing in theaters before the new Star Wars movie. The trailer debuts just as Britain's Westminster Abbey announced it would not allow Howard's movie to film there because the abbey considers the book "theologically unsound."

Bart Ehrman has written widely on early Christian documents. Like a lot of Americans, he loved reading "The Da Vinci Code," but Ehrman also immediately noticed factual errors ("howlers," he calls them). Focusing on ten issues-including the role Constantine played in the formation of the Bible and the evidence for Jesus' marriage to Mary Magdalene-Ehrman gives readers a lesson in how the Bible is scrutinized by scholars, without a theological wrist-slap. Beliefnet senior editor Deborah Caldwell recently talked with Ehrman about the "Da Vinci" errors.

What did you think of "The Da Vinci Code"?

I liked "The Da Vinci Code" as a work of fiction. But the thing that troubled me is that the fiction is allegedly based on historical fact. Dan Brown begins the book by laying out what he calls historical facts, and he includes the statement that all descriptions of art, architecture, sacred rituals, and documents are factual. The difficulty I had reading through "The Da Vinci Code" with that in mind was that most of the descriptions of ancient documents, in fact, are not factual-they're part of his fiction. But people reading the book aren't equipped to separate the fact from the fiction.

How is your book different from previous "Da Vinci Code" spinoffs?

I haven't made a precise study of this, but I think almost all of the other books are written by evangelical Christians who are concerned that "The Da Vinci Code" might lead their people astray. And that isn't my agenda at all. My agenda really is more historical-making sure people understand the historical realities of the life of Jesus, his relationship to Mary Magdalene, how we got our New Testament Gospels, why other gospels were excluded, what the role of Constantine was in the formation of Christianity. These are for me purely historical interests. And people are obviously interested; some are interested in them for religious reasons and some just because they're interested in our culture's past.

I had just published my book, "Lost Christianities," which discusses the various forms of Christianity that didn't make it from the second and third century, including the Gnostics, for example, and various Christian groups who had gospels that didn't make it into the New Testament but that supported their points of view. My editor at Oxford thought I really should read "The Da Vinci Code" because the Lost Gospels are talked about-a lot. But the things that Dan Brown says about them are wrong. And so, since this was right at the top of my head at the time, I wanted to write a book that dealt with his claims about these Lost Gospels and the Jesus they portrayed to set the record straight for people interested in knowing what really happened.

Can you outline the main points of departure between what we know historically and "The Da Vinci Code"?

Well, there are big discrepancies and small discrepancies.

Let's start with the big ones.

Some of the big ones: It's not true that before Constantine, Christians understood Jesus to be human but not divine. That's absolutely false. Most people thought Jesus was divine centuries before Constantine. Second, it's not true that Constantine decided which books to include in the New Testament; he had nothing to do with it. And the Council of Nicea didn't have anything to do with which books to include in the New Testament.

Can you explain the Council of Nicea?

It was called to resolve the issue of how to understand Jesus' divinity. Everybody at the council agreed that Jesus was divine, so it wasn't a question of whether he was divine or not divine; the question was, in what sense is he divine? There was a Christian teacher named [Arius] who said that Jesus was the first being created by God, that Jesus was a divine being created by God, that Jesus created the entire world but that there was a time when he didn't exist. And the Council of Nicea took up that issue, about whether Jesus was a created being or whether he was co-eternal with God the Father. And they decided that he was, in fact, co-eternal and not a creation of God but of the same substance as God the Father.