Deliberate mistake: In the scene near the beginning of the movie where Ben finds the pipe and finds the message by rolling the pipe on the paper, the message is long and has symbols, but it is impossible for all of that to fit in the pipe. (00:12:00)
Other mistake: When Ben is threatening to throw the flare down into all the gunpowder, knowing what would happen when the fire strikes it, there are all kinds of sparks falling from the flare down into the fire anyway. Wouldn't one of those sparks would easily have set the powder off? (00:19:35)
Continuity mistake: In the scene where Ben and Riley meet Abigail for the first time, Abigail's assistant ushers them into the office and the camera shows her walking out of the office. In the next shot you see the camera on Abigail talking to the two men. When the camera pans back to them, you see the assistant leaving the room again. (00:22:20)
Continuity mistake: When Gates and Riley are talking in front of the Lincoln Memorial, the clouds in the background change. It would be possible that they change so quickly during the shots, but only if there was a gale and not sunny weather as it is in the movie. (00:27:00)
Continuity mistake: When Riley is in the Subway to install the video feed, he places his laptop on a table. On its left side there is a little antenna. When the laptop is on the ground, the antenna is horizontal. In the next shot, the antenna is already folded out in a 45° angle. (00:30:05)
Continuity mistake: When Riley is cutting into the pipe holding the cable for the National Archives, the hole he cuts changes shape after the shot showing him examining the wires. (00:31:35)
Factual error: During the heist preparation scene, Riley enters the National Archives Metro station to record surveillance camera footage. Surveillance camera feeds for the National Archives would never be accessible within a Metro station due to both security concerns and the fact that the feeds are not needed outside of the National Archives building. (00:32:00)
Continuity mistake: When Dr. Chase is entering her password she goes for the first letter on the keyboard. Her little finger is at the right end of the space bar and her index finger is hitting the key. When the shot changes to the close-up of her hand, the little finger is in the area of the CTRL key and the middle finger is the one which hits a key, in the area of the m or comma key. (00:33:15)
Other mistake: When Abigail keys in her password to the preservation room, she only presses the keyboard 9 times including the return key. If "Valley Forge" was the password, she would have had to have used at least 12 keystrokes (including the return key.) And she never goes near the "L". (00:33:20)
Continuity mistake: When Gates takes out the champagne glass after making the fingerprints visible, the time on his watch changes from 9:11 to half past something. (00:38:45)
Revealing mistake: When Ben and Ian get the two different fingerprints from two different people, Mr. Ferguson [random security guard] and Abigail Chase, they are the exact same fingerprints. This can be confirmed on the DVD with pause and zoom. Moreover, the two scans show exactly the same emphasis/pressure on different regions within the print, with more light and detail on the left side and little in the center. (00:39:15)
Continuity mistake: When Gates enters the password he has hit the keyboard 4 times "V A (actually the "Caps lock-key, as explained elsewhere) L L" but when we see the screen with the access code, there are only 2 stars hiding the letters. (00:42:35)
Other mistake: When Gates enters the password to enter the preservation room he accidentally hits the Caps Lock key instead of the "a" key. (00:42:35)
Revealing mistake: When the two vans are driving away from the Archives, Dr. Chase tries to open the door to escape. As the camera pans from her face to the door handle, you can see by the way her hair moves that the quarter-second sequence is run in reverse. (00:48:55)
Other mistake: In the scene where Ben, Riley, and Abigail arrive at Patrick's house, the location title at the bottom of the screen says, "Philadelphia, PA." Then, as the Declaration of Independence is being examined, Patrick says that he donated the Silence Dogood letters to "The Franklin Institute in Philadelphia." Finally, as the scene ends, Ben, Riley, and Abigail are in Patrick's car, driving through the night towards Philadelphia. (00:55:55 - 01:04:15)
Continuity mistake: When the FBI storms into Ben Gates' apartment, an agent is researching the Silence Dogood letters on his Hewlett Packard laptop. However, the web browser displayed on his laptop is the Mac Safari browser. HP laptops don't run Mac software so the "photoshopped" shot of the web browser on the laptop was done on an Apple Mac. (00:57:20)
Other mistake: When Gates writes down the numbers from the back of the Declaration of Independence he forgets one number. On the document there are the following numbers: 11-6-6, 12-18-7, 14-3-7. Ben however only writes down 11-6-6, 14-3-7 and then keeps on. (01:01:10)
Factual error: Ben, Riley, and Abigail are driving into Philadelphia at sunrise to go to the Franklin Institute. They are shown driving west on the Ben Franklin Bridge. The sun is actually setting in the west behind Philadelphia, not rising. (01:07:00)
Continuity mistake: When Gates and Dr. Chase are in the store to buy new clothes, Abigail is coming out of the changing cubicle. She opens the door wing while having both hands on the edge, when the shot changes, she leans on the edge with both forearms. (01:07:50)
Factual error: The clock on the back of the $100 bill is stated in the movie to show 2:22. In reality the clock on that bill reads approximately 4:10. (01:09:45)
Answer: He doesn't simply assume "Beneath Parkington Lane" means beneath the church: Parkington Lane is the name etched on the tomb hiding the entrance to the tunnels. When he saw it, he naturally deduced what he had to do.
Sereenie