I’m not picking out specific films, just commenting on some historical inaccuracies which are common. Some have a film-making excuse (such as the lighting one), others are just plain wrong.
I’ve never used a bow, but I know that the war bows used (most famously by the English at Agincourt) in the medieval period were immensely powerful. So powerful, in fact, that a huge amount of training was necessary not merely for the skill aspect, but to have the physical strength necessary to draw one back. If an average modern man tried it, their skeleton would give way before the bow did.
Even if you were very strong, you would draw back and either loose immediately (for a high arc, aiming for a mass of men type shot) or pause very briefly to target a specific individual. You most certainly would not hold it whilst your buffoon of a commanding officer had hundreds of archers in agonising exertion because he decided to leave a huge gap between the words ‘draw’ and ‘fire’ [more on that below]. It’d be physically impossible, as well as immensely stupid.
Whilst we’re on bows, they aren’t ‘fired’. They aren’t firearms, there is literally no fire involved (unlike guns). They’re loosed or shot. This is a pet hate of mine (although it’s very easy to do it by accident, so it’s a bit more forgiveable than the idiotic idea of having men’s shoulders torn apart by needlessly holding back a fully drawn bow for half a minute).
Scots and woad do not mix. Woad was applied by Picts (the word is from the Roman name for them, the same root as the word ‘picture’, because the Picts were painted). The Scotti were a Hibernian (Irish) tribe that migrated to Caledonia, killing and conquering the Picts. As an aside, woad was antiseptic, and may’ve helped slightly with preventing wounds becoming infected.
An understandable inaccuracy relates to plate armour. Plate armour (beneath which would be mail and a quilted jacket that was, by itself, strong enough to sometimes prevent an arrow piercing the body) was bloody fantastic. Medieval knights shifted from the sword and shield to the two-handed sword because the armour was so good a shield was pretty much superfluous. Curved metal plates with mail and gambeson underneath rendered a knight almost impervious to attack (the longbow was something of an exception to this, and one reason French knights detested English archers). At Agincourt, an awful lot of French knights either drowned in mud or were stabbed in the skull (either through eye holes in helmets, or after having their helmets wrenched off). Getting through plate is a devil of a job. Something like a crow’s beak works relatively well but in a duel a sword would outclass such a top-heavy weapon.
However, in films you do have to kill and wound characters. Having everyone wander about in surprising safety would rather kill dramatic tension, so this is the most understandable inaccuracy. That said, stabbing’s the way to go if you want to knock off a knight in armour. Slash at him with a sword and you may annoy him by scratching his favourite breastplate, but bruised pride is about as far as the wound will go.
Battles often degenerate into mêlées, but this was generally not accurate. Whilst the medieval period didn’t quite have the strategy of the Greek and Roman world, tactics and battlefield deployments were not haphazard, nor did warfare regress to pre-Roman Celtic mayhem. Being together in a unit is advantageous. If you’re spearmen, you get a bristling hedge of steel to face the enemy, and a shield wall to confront their attack. If you’re archers, you get a cloud of arrows which is rather harder to avoid than just the one. Not only that, foot soldiers who are spread out are a horseman’s dream to destroy. In formation, foot soldiers can fend off cavalry with relative ease. Routed, infantry are target practice for horsemen.
There are also a number of little everyday inaccuracies, some of which are understandable, others of which are odd. Maps were pretty uncommon (there are some famous examples, such as the old mappa mundi, but these were exceptions rather than the rule). They can be useful for storytelling purposes, but mostly they weren’t needed. A man from a village would know the way to the nearest town. If he needed to go on from then, he’d ask for directions. The absence of maps and understanding of geography beyond the immediate vicinity did have occasional perverse consequences, such as the horde of peasants that followed the First Crusade asking if they were nearly at Jerusalem after a few days of walking (they weren’t).
Clothes were not bland. They were often bright colours, sometimes of differing hues. Mud-stained peasant brown was not the extent of the 14th century colour chart for poor people. (Some believe Robin Hood was actually invented by dyers to advertise their wares).
Cartwheels have spokes. This is not high technology, it’s common sense. A solid wheel weighs a lot more, creating more work for your donkey and increasing the risk of the cart sinking into mud.
Thatch has to be thick. Several feet, at least. You can’t have a few layers of straw and call that thatch because it won’t actually work.
In the modern world, we’re used to constant and widespread light. But that just didn’t happen in the medieval world. Yes, there were light sources, including the hearth, candles, lamps and torches. But these things aren’t free. The hearth devours wood, candles cost money, lamp oil is expensive (which reminds me, boiling oil wasn’t used by those defending sieges so much as boiling water or sand [much cheaper]) and torches only last thirty minutes or so.
When an explorer enters an ancient ruin and torches are burning, or a medieval clerk has eight damned candles burning on his desk or scattered about for a visually pleasing shot, it’s just plain wrong. There’s often excessive lighting in films (in modern day settings, there are sometimes half a dozen lamps in a room, or more) but it makes no sense at all in a medieval setting.