Braveheart

This is a pretty well-known downfall of Braveheart, but people still love to point it out. The film was set in the year 1300 and followed a Scottish patriot who famously led a revolt against the English army. Since he was Scottish, the main character was commonly dressed in a kilt. The folks behind the scenes must not have been paying attention to detail since kilts were actually introduced in the 16th Century, an entire 200 years after this film was set. The kilt must have been too good to pass up!