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.
The X and P seen on soldier's shields are not the Roman letters X and P but the Greek letters Chi and Rho, the first letters of the word Christos. This was the sign that the Roman Emperor Constantine had placed on his soldiers shield, and identifies the soldiers as Christians.
Although the weather seems very cold and dreary, the movie was shot during near-record high temperatures in Ireland.