Factual error: The poem Isolde recites, John Donne's "The Good-Morrow", is a 17th-century work, which is centuries later than the movie's time period.

Revealing: In the scene where Tristan and Isolde have their first secret talk in the market, when the camera is on Isolde, you can see that she is wearing contacts.

Factual error: In the scene where Tristan is making his return from Ireland and the crowd is gathering around him there are two hens in the foreground. One is a Rhode Island Red and the other is a Black Plymouth Rock. Both of these are American breeds of chicken and did not appear until many hundreds of years after this film is set.

Deliberate "mistake": The first time the warriors ride out during the full moon, the shot of the moon shows that it is in the phase of "half moon".