Continuity mistake: In the bootcamp scene where Captain Sobel is yelling at Private Christenson for drinking from his canteen, you see a machine gun resting on Christenson's right shoulder. When the camera angle changes to behind Christenson, the machine gun has suddenly moved onto his other shoulder. This happens quite a few times in this particular scene.
Continuity mistake: When Aetius is about to leave Rome, he tells Valentinian he's going to Ravenna to take command of the 3rd Legion. The banners of this legion, however, have "LEG XX" on them, which means this is actually the 20th Legion.