Collasuyu, the largest quarter, stretched from Cuzco south, was dominated by the altiplano, the breadbasket of the empire, but also included mountainous areas. Many important crops were grown in this area. Most Incan agriculture was based on the concept of verticality, which was in use in the Andes long before the Incas came to power. Mountain dwellers had a home base from which they controlled their area, on which they grew certain staples. At different times of the year, however, some family members would descend to tend crops grown at lower elevations, and to take care of herding duties at yet another level.
Verticality varies in form and intensity with elevation, aridity, topography, and other conditions.
The forested eastern flanks of the Cordillera supported more compact forms of verticality than did the arid Pacific watershed. In terms of longitude, the strategy is least pronounced in the northern equatorial zone where the mountains are low and tropical. Intensity and elaboration increase to the south and are most pronounced in the Titicaca basin and the salt puna uplands of Chile. Verticality was pursued by households, communities, and states, and at different levels of organization it assumed different configurations. The basic unit of Incan society was the alluyu, a collective of related families responsible for their land and herds.