Many of these functions were delegated to a large staff of professional administrators: priests, market supervisors, military leaders, judges, tax collectors, and accountants. The tax collectors, or calpixque, were especially important administrators because they acted as the rulers’ agents in collecting goods and services from the calpulli chiefs.
Most of these positions were appointed and selected from two classes—the pipiltin (plural of pilli), and the professional warriors. Society was divided into three well-defined castes. At the top were the pipiltin, nobles by birth and members of the royal lineage. Below them was the macehual class, the commoners who made up the bulk of the population. At the base of the social structure were the mayeques, or serfs, attached to private or state-owned rural estates. Within these three castes, a number of social classes could be differentiated, according to wealth, occupation, and political office. The Aztec system made a distinction between ascribed and achieved status. By a system of promotions, usually as a reward for military deeds, commoners were appointed to such political offices as calpixque and judges. Many pipiltin held no political office and, unless they had inherited private estates, were forced to live off the largess of the ruler. Commoners who had captured four enemy warriors in combat were promoted to the rank of tecuhtli, entered one of the military orders, were assigned a private estate with serfs for their maintenance, and acted as an elite professional army. The children of both pipiltin and tecuhtli could enroll in the religious college, or calmecac, where they could be trained as priests or political administrators. The calmecac apparently was also open to certain other commoners, such as wealthy and influential merchants and craftsmen.
Aside from the commoner-warriors, the macehual class was further differentiated into class levels. Certain occupations were accorded higher prestige than others (merchants, lapidarians, goldsmiths, and featherworkers are mentioned, and the list probably included stone sculptors); and all urban occupations were assigned higher status as compared with rural farming. Since occupations were restricted to calpulli membership and since the calpulli were kin groups, it follows that crafts tended to be hereditary. In small towns the craft specializing group would have to be the barrio pequeño. In the cities it was definitely the larger unit, but in either case crafts would be found within hereditary corporate groups.
The system of social stratification emphasized ascribed status but also permitted considerable vertical mobility. The land-tenure system was an important aspect in maintaining both processes, as could be expected in a basically agrarian society. Although most of the land was held in common by the calpulli, private estates with serfs helped to maintain the prestige of the pilli class and similar estates assigned to political office; and the tecuhtli positions freed able commoners from the necessity of subsistence procurement.
The taxation system also helped to maintain the social system. All heads of households owed military service to the tlatoani. For the pipiltin and tecuhtli, this was the only tribute demanded. Urban craftsmen also paid tribute in their craft products but were exempt from corvée labour. That obligation, plus taxes in agricultural products, were the burdens of the rural peasants, and the mayeques owed their labour and agricultural produce to their overlord.
Two other elements in the Aztec social system were pawns and slaves. The former were poor men who could sell themselves or members of their household for a specified period of time. Their rights were carefully defended by Aztec law, and they were not slaves but more like indentured servants. True slaves did exist and in some parts of Meso-America were used as workers or servants. Among the Aztec, the mayeques were their counterpart. Slaves were bought in lowland markets and used primarily for human sacrifice.
The high development of craft specialization—much of it full-time—in Aztec towns has been noted above. But many rural communities also had part-time specialities, a feature due in part to the heterogeneity of the highland environment, with its highly local distribution of resources. Foreign goods were brought into the Aztec homeland by great caravans of professional merchants called pochteca, who frequently undertook journeys exceeding a year in length. As a group the merchants enjoyed very high prestige and even had their own tribunals. Various merchant wards of a great number of towns and cities in central Mexico were organized into one great trading guild that had its centre at Tenochtitlán. They also organized and administered the town markets, another highly evolved aspect of Aztec institutions. These markets were held in great open plazas—in smaller towns every fifth day, in larger towns and cities daily, although in the latter case the market population reached a peak every fifth day.
The centres and the political organization of large states such as the Aztec empire were fundamentally similar in character to small ones; but the vast differences in size (Tenochtitlán, the Aztec capital, may have had 140,000 to 200,000 inhabitants in 1519) demanded some changes. Generally, when one central Mexican state conquered another, the ruler of the conquering town extorted an annual tribute, but there was little attempt at political integration. In the case of the Aztec, this policy was generally maintained, but many conquered states were given Aztec governors. Furthermore, conquest was usually accompanied by an exchange of women from the two ruling lineages (conqueror and conquered), and successors to the throne of the conquered states were through these women, from the royal lineage of Tenochtitlán. As a result, the ruling class gradually tended toward a single kin group. Because of the great number of states conquered by the Aztec (400 to 500), some form of intermediate-level territorial and administrative organization became imperative. The states conquered by the Aztec were grouped into 38 provinces. One town in each province served as capital, and an Aztec tax collector-governor was placed there to supervise the collection, storage, and disposition of the tribute. In many provinces, the Aztec established garrisons. These consisted of warriors and their families culled from all of the towns of the Valley of Mexico, and they were assigned lands in the conquered province. Since they supported themselves, they were colonists as well as troops. The planting of colonists, combined with such factors as the merchant guild and royal family intermarriage, suggests that the Aztec elite were attempting to integrate more closely the population of the Valley of Mexico as a kind of core nationality for the empire. Other indications that the Aztec were in the process of achieving further political integration are statements in several relaciones that the tax collectors served as courts of appeals in serious judicial cases and also that the Aztec introduced the cult of their national god Huitzilopochtli to conquered provinces. Tenochtitlán