Foederati

To the Romans, all conquered people were considered to be barbarians. Unfortunately for Rome it became impossible to defend all their conquered domains with Roman soldiers. Rome therefore did the next best thing by employing locals to do their dirty work for them. The pay usually consisted of plots of land. This process of employing mercenaries or foederati cost nothing as they were giving them the land they had taken from them in the first place. The practice of employing foederati was used by Rome all over Europe.