Factual error: The Liberty Bell is depicted ringing as the Declaration of Independence is being signed on July 4 (a mistake itself) in the film. The bell actually did not ring on that date, but on July 8, when the Declaration had been returned from the printer and unveiled to the public.
Revealing mistake: In the opening scene, when the soldiers and slaves march down the mountain, as the carriage containing Aguirre's daughter passes by the camera, one of the soldier extras just behind the carriage looks directly at the camera. (00:03:38)