Factual error: One of the naked female dancers at the party has breast implants. Although some forms of plastic surgery were known to the Romans, breast augmentation was not one of them. If you want to check for yourself she appears just after the masked dwarf moves through the shot.
Factual error: During the final battle as Saxa starts using the ballista against the Romans in the front, the ballista is portrayed as a weapon launching multiple projectiles at once, while in reality it only launched one at the time.
Factual error: When Numerius wants Spartacus to kill Varro, he gives a thumbs-down. People who wanted to see a defeated gladiator slain would express their desire with a thumbs-up gesture instead.
Factual error: When Lucretia is attending the market she is wearing high heel shoes which did not exist at the time, and weren't invented until the 15th century.
