The bulk of the Aztec population consisted of commoners who lived in hamlets cultivating chinampas and fields allocated to their families by community groups known as the calpulli. Originally, calpulli (“big houses”) were clans or groups of families claiming descent from common ancestors. With the passage of time, ancestry became less important to the nature of the calpulli than the fact that groups of families lived together in communities, organized their own affairs, and allocated community property to individual families.
Apart from cultivating plots assigned by their calpulli, Aztec commoners worked on lands awarded to aristocrats or prominent warriors and contributed labor services to public works projects involving the construction of palaces, temples, roads, and irrigation systems. In times of war, the calpulli went into battle as a unit of about 200 to 400 men. Each calpulli was also attached to a noble house, which distributed land in return for tribute. Cultivators delivered periodic tribute payments to state agents, who distributed a portion of what they collected to the elite classes and stored the remainder in state granaries and warehouses. Nobles would be distinct from commoners by their ability to build two-storied residences. However, if a noble died without descendants, his land would revert to the calpulli.
Commoners had a limited ability to move in either direction in social rank. Upward mobility was achieved through achievement and service to the state, usually in war, religion or trade. They could become quauhpipiltin, or “eagle nobles”, meaning they were nobles only for their lifetimes.
In contrast, Aztec society included slaves, who usually worked as domestic servants. Most slaves were not foreigners, but Aztec. People became slaves through debt or punishment, but not through birth; slavery was not hereditary. Slaves could marry, have children (who were free) and even own property. Anyone could own a slave, but most slave-owners were nobles. The owner was responsible for feeding and housing the slave and had control over the slave’s labor. People sold themselves into slavery when they could not support themselves. During the great famine of the 1450s, for example, many Aztecs sold themselves to people of the Gulf Coast where economic conditions were better. Failure to pay taxes was another way to become a slave, with the purchase price going to cover the debt. Some other crimes were also punishable in this way. The change in status from free citizen to slave was an official act that had to be witnessed formally by four officials. Some pochteca merchants specialized in trading slaves, and several markets were known as centers for the slave trade. Slaves for sale were identified by large wooden collars [to make escape more difficult from the market].