How did irrigation support cities on the coast of Peru?

In the arid coastal environment of Peru, sophisticated irrigation systems were essential for supporting concentrated populations and the development of urban centers. Because only a few of the rivers descending from the Andes to the coast flow year-round, ancient societies engineered complex networks to manage scarce water resources.12

These systems allowed for the cultivation of otherwise inhospitable desert lands, providing the agricultural foundation necessary to sustain large, hierarchical states such as the Moche and the Chimú. In many northern valleys, these irrigation works reached their maximum extent, with engineers sometimes connecting multiple river systems—such as diverting water from the Chicama Valley to the Moche Valley—to ensure a reliable supply for cities like Chan Chan.123

While these systems enabled the growth of monumental architecture and urban life, they also created a strategic vulnerability; the dependence on these elaborate, centralized water networks made coastal polities susceptible to military conquest, a factor that facilitated the Inca expansion into the region.23