Corrected entry: Near the end of the movie, just before the fight in the beach, Robin is riding his horse on top of the cliff. In the next shot, just a few moments later, he is in the beach leading the attack. There is not enough time for him to go down the cliff.
Corrected entry: English archers repelling the French Army landing are lined up, single file, along the cliff's top edge. Wrong. One, they are shooting arrows into a prevailing on-shore wind, therefore, highly unlikely that their arrows would reach the French at water's edge; two, the archers are congregated into a block so that their arrows would arrive in a thick "hail"; and three, after launching their arrows, archers were expected to join the fray, something that they could not do in a timely manner.
Corrected entry: French Army landing: Horses get sea-sick and the English Channel is a very rough body of water - therefore, it's highly unlikely that knights would be able to ride their horses off the landing barges into battle.
Corrected entry: Right after his coronation, John calls out to his mother. Eventually saying that she supported him at all times, even during his four-year imprisonment in the Muslim lands. These four years however, where just two. 1192 - 1194.
Corrected entry: When Maid Marian goes to see what is happening outside of her farm at night, she strings her longbow by bending it against the ground with one hand. It is difficult enough with the correct method (using your legs as a lever, and bending the bow with both hands). To string a 6 foot English longbow from that time the way Maid Marian did would be impossible.
Corrected entry: When Prince John and his French girlfriend are discussing politics, she uses French and a French accent to indicate her Frenchness. But in 11th or 12th century England, French was the language of royalty. That is all of the royal family spoke French as their first language. Thus we get Anglicized words like royal, viscount, earl and food words like beef (instead of cow), pork (instead of pig) etc, etc.
Corrected entry: In the beginning of the movie, when thieves steal Marianne's grain, she says the word "bastard". However, the word "bastard" didn't originate until the second half of the 1200's.
Corrected entry: When Robin and the boys are being rowed up the Thames, the captain tells Robin "we dock in 20 minutes." Mechanical clocks weren't in Europe until the 1300s and they were cumbersome affairs. No one could have told time by the minute on-board ship in the 12th century.
Corrected entry: In the teaser trailer as the Frenchmen are attacking the beach, one of them has a shield that is visibly flapping, as if it is made of wet cardboard rather than wood.