Aztec society was divided into a number of classes. Although people could advance to a higher level, most often by distinguishing themselves in battle, the usual pattern was for individuals to live out their lives in the class into which they had been born. At the top of the social order were government officials and priests. Next came traders and craftsmen. A special group of traders called pochteca brought luxuries such as gold, gems, and exotic feathers from distant areas and served as military spies. Below these groups were the farmers, who composed most of the population. Lowest in society were the slaves. Some slaves were captives or criminals, but most of the slaves were poor people who gave up their freedom in exchange for food, shelter, and clothing. They usually served as slaves for only a short period of time and were well treated.