Outlaw King very clearly aimed at avoiding Braveheart-type fantasies (being set right after that latter film's historical events), by displaying era-accurate attires and weapons for the most part, looking far more realistic than most period pieces set in the medieval era in this regard. In fact, there are very small, specific details of medieval life that the movie goes out of its way to showcase.
- As pointed out by Shadiversity, there's a heavy use of the padded cloth armor piece known as the gambeson, which is a very rare thing to see in films and series despite how overwhelmingly common it was in Middle Ages (it was cheaper to make than mail armor, lighter to wear and almost as effective).
- The film doesn't overly sugar coat the cause of the Bruce and his men, showing some of the underhanded tactics they made use of, such as murders in churches (which were holy places, committing such acts in them had severe moral consequences).
- The idea of "raising the dragon", a reference to showing no quarter to the enemy.
- The scene in which Prince Edward swears by two swans actually happened in a famous event known as the Feast of the Swans.
- Robert and Elisabeth are married underneath a shroud.
- During dueling scenes, the characters always step forward or backward or twist their hips with a strike, an important aspect of pre-modern fencing that many fight choreographers often overlook.
- Robert Bruce often fights with a one-handed axe, as he is noted to have done in historical records.
- The armies of both England and Scotland do not march under national flags, but banners depicting the personal heraldry of the nobles leading them. To wit: Robert initially marches under the Bruce's emblem (a red saltire on a yellow field) but after his coronation he switches to the Royal Standard of Scotland (a red lion rampant on a yellow field, bordered by red fleur-de-lis, as seen on the page image).
- Likewise the characters who are nobles tend to bear shields and tabards displaying their personal heraldry, which is also represented accurately. This includes the Captain America-like shield of Black Douglas, with three white stars on a blue top stripe, as surprising as it may be.
- Robert was indeed crowned by a woman, as unusual as it may seem (and was) for the period.
- Prince Edward briefly talks to one "Piers" at the start of the film. This is Piers Gaveston, the Prince's alleged lover in medieval accounts and the inspiration for the guy Longshanks infamously throws out of a window in Braveheart. While Edward II's sexuality is debated by modern historians (they may just have been Heterosexual Life-Partners who got slandered by their enemies, which wasn't uncommon in the sordid rumor-mill of Medieval politics, and both fathered children, in any case), it simply isn't brought up in this film, unlike his Camp Gay portrayal in Braveheart.
- King Edward did by one account call for his bones be brought into battles against the Scots, though there are other stories of what he asked to be done with his remains.
- Robert speaks to some Frenchmen who wanted to join his cause in their language. French was the primary language of European aristocracy at the time.
