Historical accuracy
Randall Wallace, the writer of the screenplay, has acknowledged Blind Harry's 15th century epic poem The Acts and Deeds of Sir William Wallace, Knight of Elderslie as a major source of inspiration for the film.
Scottish historian Elizabeth Ewan describes Braveheart as a film which "almost totally sacrifices historical accuracy for epic adventure". The title of the film is also historically inaccurate as the "brave heart" refers in Scottish history to that of Robert the Bruce, and an attribution by William Edmondstoune Aytoun, in his poem Heart of Bruce, to Sir James the Good: "Pass thee first, thou dauntless heart, As thou wert wont of yore!", prior to Douglas's demise at the Battle of Teba in Andalusia.
Historian Sharon Krossa notes that the film contains numerous historical errors, beginning with the wearing of belted plaid by Wallace and his men. She points out that in the period in question, "no Scots ... wore belted plaids (let alone kilts of any kind)." Moreover, when Highlanders finally did begin wearing the belted plaid, it was not "in the rather bizarre style depicted in the film." She compares the inaccuracy to "a film about Colonial America showing the colonial men wearing 20th century business suits, but with the jackets worn back-to-front instead of the right way around." She remarks "The events aren't accurate, the dates aren't accurate, the characters aren't accurate, the names aren't accurate, the clothes aren't accurate—in short, just about nothing is accurate." The belted plaid (feileadh mor) with the baldric (leine) was not introduced until the 16th Century.
In 2009, the film was second on a list of "most historically inaccurate movies" in The Times. In the 2007 humorous non-fictional historiography An Utterly Impartial History of Britain, author John O'Farrell notes that Braveheart could not have been more historically inaccurate, even if a "Plasticine dog" had been inserted in the film and the title changed to William Wallace and Gromit.
Screenwriter Randall Wallace is very vocal about defending his script from historians who have dismissed the film as a Hollywood perversion of actual events. In the DVD audio commentary of Braveheart, director Mel Gibson acknowledges many of the historical inaccuracies but defends his choices as director, noting that the way events were portrayed in the film were much more "cinematically compelling" than the historical fact or conventional mythos.
Portrayal of Robert the Bruce
The portrayal of Robert I of Scotland (Robert the Bruce) in the film is considered by historians to be wildly inaccurate. In particular, his taking the field on the English side in the battle of Falkirk is completely fictitious; Bruce was not present at Falkirk. Although he repeatedly changed alliances between the Scots loyalists and the English, mostly for political reasons, Bruce never betrayed Wallace directly.
Portrayal of Prince Edward
The depiction of the Prince of Wales (the future King Edward II) as an effeminate homosexual in the film drew accusations of homophobia against Gibson. The real Edward II did father five children by two different women, but was also thought to have had sexual affairs with men, not least with Piers Gaveston. Gibson replied that "The fact that King Edward throws this character out a window has nothing to do with him being gay ... He's terrible to his son, to everybody." Gibson defended his depiction of Prince Edward as weak and ineffectual, saying,
I'm just trying to respond to history. You can cite other examples – Alexander the Great, for example, who conquered the entire world, was also a homosexual. But this story isn't about Alexander the Great. It's about Edward II.
Gibson asserted that the reason that Longshanks kills his son’s lover is because the king is a "psychopath". (This is another inaccuracy as Piers Gaveston lived on into the reign of Edward II.) Gibson expressed bewilderment that some filmgoers would laugh at this murder:
We cut a scene out, unfortunately . . . where you really got to know that character (Edward II) and to understand his plight and his pain. . . . But it just stopped the film in the first act so much that you thought, 'When's this story going to start?'
http://en.wikipedia.org/wiki/Braveheart#Historical_accuracy