Visible crew/equipment: In the famous scene where the wall collapses onto Keaton and he passes through the open window as it falls, look around the center of the window just as the wall starts to fall. You can briefly see a crew member, who has just pushed the wall, run for cover.
Factual error: The movie is supposed to be in the 15th century. In a scene we see a priest, wearing a Jesuit robe. But the Jesuit order was founded in the 16th century. So it's impossible that a priest wearing a Jesuit robe appears there.