Anachronisms: In the 15th century, a priest can be seen wearing a Jesuit robe. The Jesuit order was founded in the 16th century.
Revealing mistakes: Near the end of the film when two rocks are thrown through what is supposed to be a leaded glass window it is clear from the way it breaks that it is just a regular pane of glass with lines drawn on it to simulate leaded glass.
Anachronisms: The soldiers wear helmets with modern chin strap fasteners (likely WW1 British infantry helmets). Those helmets could be a deliberate anachronism though.