Factual error: The Viking style funeral that Robin's adopted father has would have been unthinkable at the time. Cremation wasn't just against the law, it was completely against the teachings of the Church. He would have been interred in the family crypt or, if that had been destroyed, buried.
Factual error: The invasion was supposed to be at Dymchurch, as mentioned in the Blue Ray director's cut version. In the film, the invasion area is a sandy beach flanked by cliffs. In reality Dymchurch is a pebble beach and is on the edge of the Romney Marsh with no cliffs. The lack of cliffs can be checked via OS Maps of the area.
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Factual error: The French invade the lands of England by crossing the English Channel. The kings of England considered Normandy, Gasconie and Aquitane to be their primary lands up to defeats in the Hundred Years War, about 230 years after the movie takes place. French invasion of England would be illogical and impractical, if not downright suicidal. Not surprisingly, English holdings in France aren't mentioned as a target.