I've read somewhere that Athens employed Skythian archers as a police force and city garrison. Those guys were apparently slaves, but there must have been a reason why they were so trusted and valued by their Athenian masters. There were originally three hundred of those slave soldiers in the city's service, but that number was later increased to nine hundred. In peace time, they would act as an escort for the city's archons and magistrates. And even went as far as being used as a form of crowd control during festivals and Boule sessions. In war, two hundred of these men would be mounted and employed to act as auxilliaries for Athen's one thousand strong hippeon corps. Just a thought.