Constructed around 256 BC, Dujiangyan is the world’s oldest irrigation system that is still in use today. Long before the invention of gunpowder, the system was using natural topographic and hydrological features to divert water from the Min River for irrigation and flood control without the use of dams. To this day, the ecological engineering feat irrigates 668,700 hectares of farmland in the Chengdu plains of southwestern China. It was in the tranquil, lush mountains surrounding Dujiangyan...