"The DaVinci Code [sic] is a fictional book and movie. And while it does take some things from history that sound good and like evidence, Dan Brown takes liberties with the actual facts in order to tell his story. For example, Constantine did not approve what chapters went into and which were excluded from the New Testiment."
Here's something that is true of anything that's historically related to Christianity, but isn't directly referenced in the Bible: The history we all believe is the culmination of years and centuries of written and oral records, passed on from person to person. It is only as accurate as the veracity of the person or persons recording the event.
Now Dan Brown wasn't standing behind Constantine, chronicling his influence on the Bible. But then, neither was anyone else alive today. Nor was anyone who's lived in the last 1800+ years. Everything we know we know from history, and the writers who passed on the stories from year to year. And the truth is, while it may be an "accepted" historical fact that Constantine didn't do what Dan Brown _fictionally_ supposes he did, nobody can really sure.
History is always at best tenuous. What we believe is true is always subjective due to the most powerful influence of the time. The old adage is correct: "The winners write the history books".
Now, the more eyewitness accounts to an event the better the chance the history is correct. Everyone believes the Japanese attacked Pearl Harbor on 12/7/1941. There were tons and tons of people who either witnessed the attacked or reported on it. But who knows who fired the first shot of the Revolutionary War? Was it Bell or Watson who really turned the final screw and invented the telephone (it could've ultimately been Watson that said, "Mr. Bell, come here - I need you")? Who was responsible for committing Christian forces to the Crusades?
History has a lot of questions, and a lot of facts taken as fact due to tradition. Maybe they're exactly true, maybe they aren't. But until a Doc Brown really perfects the De Lorean time machine, there's no way to be absolutely certain what happened when the Bible was first put together. We can believe, and accept that what happened is correct (and it most likely was) but to blindly dismiss any other historical possibilities that far in the past, even fictional ones, is disengenous and close-minded.
Those who forget history are bound to repeat it - but history may not be exactly what you think it is...