Gladiator was bad, bad. I never got as far as is it conforming with history; the acting made me wish I had been sacrificed. Braveheart was not so bad, and probably not very accurate either, but hey, with an ending where the hero is hanged, drawn, and quartered, what's not to like?

On the other hand, for a really, really terrible performance with little or no relation to anything, try Excaliber. Even the music was wrong. If I recall correctly, the legendary Arthur was fighting Saxons, but the Arthur music is quite often Wagner. Wasn't he the Teutonic myth guy?