Continuity mistake: Near the start, right after Spartacus slices a man, you see him holding only the hilt of a sword - when shots of cutting are seen, the blades are normally added digitally, but it wasn't in this case. A couple of seconds later it is back to a full sword. (00:01:40)
Continuity mistake: During the final battle there is a long trap between the armies, filled with spears and hidden, where the Romans fall when trying to get to Spartacus' army. Before the Romans pass into it, a messenger from the Roman army comes through on his horse without falling into this long continuous trap.