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.
Continuity mistake: From the time Attila became king of the Huns to his death, he does not age.
Continuity mistake: When Attila has killed his brother in a duel, he claims N'Kara and goes raiding villages. If you look closely, you can see that he's already carrying the 'sword of the war god', although at that point of the story he hasn't found it yet. He finds it later, after N'Kara has died giving birth.