The main uncertainty about Spartacus is his ethnicity. He is called a Thracian, but Thracian is both an ethnicity and a style of combat in gladiatorial games. Gladiators were organised by their combat style, and by that point in Roman history gladiators were no longer limited to just their cultural combat style, especially if the slave was not one of the traditional enemies of Rome. So while it is possible that Spartacus was from Thrace, it is equally possible that he was from pretty much anywhere else, and simply trained in Thracian-style combat as a gladiator.