Corrected entry: Crassus, when talking to the man he makes the head of the Roman Garrison, says that the reason he is doing this is to 'checkmate' his senate opponent. 'Checkmate' is a chess term and as such would not have been used by a Roman in the 1st Century BC as the game wasn't invented until at least the 6th Century AD in India.
Corrected entry: In the scene where Gracchus is giving money and travel permits to Batiatus and Varinia, he mentions that one of his innumerable cousins is the Governor of Aquitania. Aquitania would not become of a province of the Roman Empire for more than 40 years following the time of Spartacus' revolt.
Corrected entry: If you look at the legions of Roman soldiers at just about any point in the film, they're wearing wristwatches and trainers.
Corrected entry: This is more of an omission rather than a mistake. One of the reasons why Spartacus and his army was defeated was the internal strife between Spartacus and his lieutenant, Crixus. According to Greek historians, Appius and Plutarch, Spartacus wanted his army to leave the Italian peninsula and go to Gaul so the army can be disbanded. After disbanding, Spartacus wanted the slaves to go home to their countries of origin. However, Crixus wanted to stay in Italy and keep on pillaging. The Roman generals used this internal strife to their advantage and defeated Spartacus' army. The movie makes no mention of this very historically significant internal strife.