That's a very good question. As far as the story goes, it is very accurate...however much like all Hollywood movies, they had to add their own flavors. For instance, Colonel Chamberlain's 'side-kick' (the Irish guy) never existed. He was created in order to add some spice to the film. Another fault is the scenery. Of course, Gettysburg battle-field looks nothing like it did in the 1800's. Also due to filming, and the large crowds which gather there all year long, they had to film in areas which may have been similar to engagements which happened at Gettysburg. Since there are thousands of monuments and erected stone figures all over Gettysburg, most of them had to be covered with a camouflage mesh during filming.
The director of the film did an excellent job picking out actors which actually reflected pictures of the actual Generals, etc. That was surprisingly accurate. Now, this movie was mainly a take-off of the novels "Gods and Generals" and the "The Blue and the Grey". But what the director tried to do was actually incorporate diaries from people like General Lee and such. This was so he could grab the attention of the Gettysburg historians and fanatics like myself.
The best way I can describe it is if you are actually on the battlefield. I live 45 minutes north of Gettysburg, and if anyone would ever get into that area, look me up. My dad and I are known to give the best tours and we don't even work for the National Park service

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