Dark Sun: Seared to the bone
City dwellers who aren’t templars, nobles, affiliated merchants, or slaves are citizens. Independent merchants and artisans make up the bulk of this class. Mercenaries, minstrels, monks, priests, masters of the psionic arts, and adventurers or others who wield extraordinary powers make up the rest.
These people are free, but only until a capricious templar or noble judges them guilty of a crime. When that happens, a free citizen becomes a slave. However, this fate usually befalls only the powerless citizens. Those who can defend themselves are rarely harassed by templars, who do not wish to risk losing several soldiers just to acquire one slave.