Raised field agriculture was abandoned before or soon after the Spanish conquest, and most of the fields were converted into pasture for colonial haciendas and became government cooperatives in 1968. We found that rebuilding and using the fields was the best way to understand raised field agriculture (Fig. 4, Color Plate 13). From the beginning, local farmers were active participants in this experimental research. Through archaeological investigation and agronomic experimentation, we determined that raised fields resolved many of the problems facing farmers at high altitude (Fig. 5). Through raising the platform, farmers doubled the depth of topsoil for crops. The elevated platforms created dry surfaces in the waterlogged and flooded lake and river plains. The water-filled canals beside the platforms provided moisture for droughts during the growing season. Heated by the sun during the day, the water in canals protected crops against the killing frost that is common at high altitude. In addition, the canals captured nutrients and produced organic-rich sediments that could be incorporated into the fields for sustained harvests. During the first few years after reconstruction, the experimental raised fields produced harvests two to three times that of nonraised fields (Fig. 6).