Baopingkou

Baopingkou, or the Treasured Bottle Mouth, is a narrow channel carved directly through a mountain ridge between Yulei Mountain and Lidui. Seen from above, the passage resembles the neck of a bottle, an shape that serves as a vital regulator for the entire Dujiangyan irrigation system. Built around two hundred fifty-six BC under the direction of the engineer Li Bing, the channel was cut into the rock manually using fire and water to heat and crack the stone.