Centuries later, Spanish chroniclers wrote of a centuries-old tradition honored by coastal Chimu lords, who ruled over a powerful north-coast kingdom conquered by the Inca in the 1560s. The Chimu allowed the farmers living the farthest downstream to water their fields first. Their Moche predecessors probably followed the same practice, which made economic and political sense, partly because the most powerful rulers lived downstream. As the sixth-century drought intensified, this long-established policy faltered. The diminished runoff barely watered the rich farmland far downstream. No water reached marginal fields at the edges of the valleys. Kilometers of laboriously maintained irrigation canals remained dry. Blowing sand cascaded into empty ditches. By the third or fourth year, as the drought lowered the water table far below normal, thousands of acres of farmland received so weak a river flow that unflushed salt accumulated in the soil. Crops withered. For the first few years, the lords retained firm control by carefully husbanding the grain supplies stored by the state against lean years. Fortunately, the Pacific fisheries still provided ample fish meal-until El Nino came along with unpredictable irregularity.

We do not know the exact years during the long drought when strong El Ninos struck, but we can be certain that they did. We can also be sure they hit at a moment when Moche civilization was in crisis, with grain supplies running low, irrigation systems sadly depleted, malnutrition widespread, and confidence in the rulers' divine powers much diminished. The warmer waters of the Christmas Child now reduced anchovy harvests in many places, decimating a staple of both the coastal diet and the highland trade. Torrential rains swamped the Andes and coastal plain. The rivers became raging torrents, carrying everything before them. Levees and canals overflowed and collapsed. The arduous labors of years vanished in a few weeks. Hundreds died. The survivors moved to higher ground where they camped under temporary shacks.

El Nino devastated the valley landscape. Dozens of villages vanished under mud and debris as the farmers' cane and adobe houses collapsed and their occupants drowned. The floods polluted springs and streams, overwhelmed sanitation systems, and stripped thousands of acres of fertile soil. As the water receded and the rivers went down, typhoid and other epidemics swept through the valleys, wiping out entire communities. Infant mortality soared. Cerro Blanco suffered badly. Floodwaters covered parts of the city with as much as ten meters of alluvium, stripping away five meters of soil or more in other places. The river eroded away much of the huacas, turning them into crater-sided hills.

The valley soils were so dry that much of the surface water soon vanished into the ground, turning the devastated floodplain into hardened mud. The coastal fisherfolk did not starve, for they could subsist off the unfamiliar tropical fish that now visited coastal waters. However, even a full-strength anchovy harvest could not feed the entire Moche farming population. We can be certain that several years of hunger gripped the kingdom, the flood damage aggravated by the ongoing drought. All the rulers could do was to muster the enormous, if weakened, labor force at their disposal. Teams of villagers set to work building entirely new irrigation systems adapted to tortuously changed topography. Some of these canals and field systems can still be traced on the ground today. Meanwhile, the lords sought assistance from distant allies in the highlands to the east, who had developed more drought-resistant forms of maize, with large cobs and more kernels. The new strains appear in archaeological sites dated to soon after the flood.

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