National Geographic : 1942 Feb
Who Built These Astonishing Examples of Irrigation Skill on Luzon? When and How? Nobody Knows! Pagan hill folk, with back-breaking effort, began the monumental work perhaps 20 or 30 centuries ago. Whywere terraced rice paddies built way uphere at Banaue? One theory is that lowland peoples fought the hill tribes and held them in the mountains. To get food, they evolved this ingenious agriculture. Miles and miles of dikes hold water on the level patches, floods being carried off in cleverly built spillways and tunnels.