Corrected entry: The post of 'Sheriff of Nottingham' was not created until the fifteenth century. The county had a Sheriff for centuries beforehand but from watching this film you'd think that the city alone was under his sole authority which it definitely was not. Yes it's standard movie lore, but that doesn't make it less of a mistake.
Corrected entry: When Robin uses the "telescope" by the laws of physics the image should appear upside-down. Yet the image incorrectly appears right-side-up.
Corrected entry: By the time Robin and Azeem reach England, they have been traveling together for four months. And yet, in the scene by the wall, Robin asks Azeem very personal (and expositional) questions that he definitely would have asked earlier during those four months. Why were you in jail, what does your name mean, etc.
Corrected entry: The Sheriff tells two girls to be at his room at 10:30 and 10:45. The concept of the 24 hour clock had not yet been thought of - it was thought of by a group of monks who needed to know when to start their morning prayers in the 1330's.
Corrected entry: The Sheriff says something like "It's a wonder I'm still sane." at one point. Surely the concept of sanity didn't come about until centuries later?
Corrected entry: The portrayal of the Celts is not particularly accurate. The Celts were not even that wild or barbarous when Caesar first encountered them in 55 BC. During the Roman occupation many Celts became Romanised and "civilised." By the 12th century most Celts lived in the North, the West (Wales), or the Southwest (Cornwall), but other than their language, they were basically the same as anyone else in the country. They weren't wild men living in the forest wearing animal skins. They look more like Picts than Celts, although there were no Picts like that by that time either, and the Picts were definitely not Celtic.
Corrected entry: The first person to use sutures on wounds - instead of cauterizing them with boiling oil or some such thing - was Ambroise Paré, who lived from 1520-1590, after the time period in which the sheriff is shown having his wound stitched.
Corrected entry: In the scene where Robin is taking a bath at the foot of the waterfall, you can see a tan line from swim trunks when he walks under the waterfall.
Corrected entry: In the scene where Robin shoots his arrow to cut down Wolf from the noose, we get a close up side view of the arrow flying. The arrowhead is slid over the shaft - this is different than the way they were making the arrows in the camp. In this scene they were making a type of arrowhead that is fitted into the split shaft and tied on.
Corrected entry: Azeem first wounds the witch with the spear outside the room that Marian and the Sheriff are being married in. Then in a later scene when the witch attacks Robin, and Azeem kills her with his sword she has miraculously made it back into the room even though Azeem has not yet broken down the door.