Something I've noticed since joining this site is the non-capitalization of the term "rebels" and it bugs me. This is grammatically incorrect for the most part. Before I became an evil attorney, I received a Masters Degree in American History specializing in the Civil War era, so needless to say I've read and written quite a bit about "Rebel" armies, haha. At any rate, when you are referring to something that is a unique entity, in our case we are usually referring to Spartacus' army, you capitalize it. This goes for both proper nouns (the Rebels launched the attack) and proper adjectives (Agron was a Rebel general). You don't capitalize it when you are using it as a common noun (Grandpa shook his fist and yelled "stop acting like such a rebel").
To put it another way, use the same grammatical rules you would use if you were writing about the American army e.g. "George S. Patton was an American general" or "the American army landed at Normandy on June 6, 1944".