Revealing mistake: When Lucan draws the ring of dead Dagonet's finger, you can see the finger move and keep its position. (01:14:00)
Revealing mistake: Despite at least two days of near blizzard conditions there is never more than a few inches of snow on the ground. The amount of snow we see falling should have left well over a foot of snow.
Revealing mistake: Just before the battle of Maldon, the British spy climbs into the big tree and you can see the tree is fake. The spy isn't actually climbing the tree (by grabbing branches), he's using some kind of ladder. (01:36:55)