pretty much all movies like this are historically inaccurate. They all say they are "based" on historical fact but that really means very little. I agree that that movies like this and 300 are cool as hell but if you want accurracy then read a book... Movies serve one purpose, to entertain, and we all know that we'd rather see a crazy viking that is 7' tall and wears armor that realistically weighs 4 times his body weight than watch some dudes run around in primitive outfits and rusty iron swords.
The only movie imo that effectively told a realistic story in this genre was braveheart. but even this movie had its historical inaccuracies.