The New Yorker's Peter J. Boyer on Dan Brown's dubious claims about The Da Vinci Code:

The ostensible veracity of Brown's history, if not his theology, had been part of the book's allure. Brown had asserted this veracity both implicitly (through the device of assigning historical exposition to his fictional scholars) and explicitly (beginning the book with a fact page that erroneously asserted, for example, that his shadowy Priory of Sion -- a European secret society founded in 1099 -- is a real organization). Book reviewers had praised his research, and Brown, in promoting the book, vouched for its validity; he told Charles Gibson, on "Good Morning America" that if the book had been nonfiction his factual assertions would not have changed.