I disagree. I'm not certain that either Jesus or Mary Magdalene existed, let alone that they were married, let alone that they had children and that their descendants survive today. And even if they did I don't assign any special qualities to anyone just because of their ancestors. And the Grail was invented in the 12th century by Chretien de Troyes. And a grail is a cup or chalice. And the business about "san graal" ("holy grail") being a misreading of "sang raal [sang royal]'" ("royal blood") which Brown borrowed from Baigent, Leigh and Lincoln, although it's miles more clever than anything Brown will ever think up on his own, is still just clever silliness. And the Priory of Sion was invented in the 1950's by a Frenchman trying to pass himself off as a descendant of the Merovingians and a figure prophesied by Nostradamus. And besides the factual errors Brown insists are facts and which are crucial to the plots of his stories, his books are riddled with errors which are unimportant for his plots. For example, there actually is no academic discipline called symbology, which is practiced by Brown's protagonist Professor Robert Langdon. There is, however, an academic discipline which studies symbols. It's called semiotics, and, ironically, there is an actual Italian professor of semiotics named Umberto Eco who writes fanciful novels, often having to do with wild speculations about the history of the Roman Catholic Church, which are much, much, much better than Brown's,and although Eco's fiction is infinitely more realistic and informative about the reality of both the present and of bygone ages than Brown's, he doesn't have the bad taste to try to pass any of it off as factual, as Brown does with his unfortunate piles of awkward sentences.
Just in case this wasn't already clear: I think Dan Brown's books are badly-written and that people could get a lot more entertainment as well as lot less misinformation from books written by -- well, from books written by just about anyone else.