Factual error: In one scene, focused on a period wood-staked pickup truck parked on the street, you can see clearly a modern Jeep Grand Cherokee parked on the other side of the street.
Continuity mistake: At the very beginning, when Quaid has finished showering and is picking his phone, wallet, badge, keys, etc, there is a shot of his hand as it is picking up his cellphone. Cut to a wide shot of him and the objects have moved. For example, the coins have become a close cluster, his pack of cigarettes is no longer on the newspaper, and his badge has switched places with the lighter. (00:02:45)
Character mistake: While examining "Diagramma della Verita" in the Vatican archives, Langdon is careful to use a cotton glove and a pair of tongs to turn the pages. But when he returns later to search the Bernini texts for clues about the "fire" church, he turns the book pages with his bare hands. (00:36:30 - 01:04:55)