Ioan Gruffudd was spotted curling his eyelashes by Ray Winstone one morning before shooting. Winstone spread the word, and Gruffudd earned the nickname "Sir Lashalot" for the duration of the shoot.
The horse ridden by Bors (Ray Winstone) in the film is the same horse that was ridden by Maximus (Russell Crowe) in Gladiator (2000).
The language spoken by the Woads in the film is a combination of ancient Gaelic and ancient Welsh, as the actual language spoken by the Picts has been lost.
Stellan Skarsgård turned the role of Cerdic down three times before director Antoine Fuqua was able to persuade him to take it. Fuqua never approached any other actor for the part.
Clive Owen got the role of King Arthur after Russell Crowe, Mel Gibson and Hugh Jackman turned it down, and producer Jerry Bruckheimer vetoed the director's choice of a then comparatively unknown Daniel Craig because he was convinced Owen was going to be the next James Bond.