The Beijing-Hangzhou Grand Canal is the longest artificial river in the world, spanning over 1,100 miles. But traversing China's varied topography was no easy feat. Long before the widespread adoption of modern pound locks—which use enclosed chambers to raise or lower water levels—imperial engineers relied on an ingenious, somewhat terrifying solution known as Haoba, or stone slope locks.
A Haoba was essentially a massive double slipway built out of polished stone blocks, constructed at points where the canal's elevation shifted abruptly. Instead of waiting for water to fill a chamber, crew members towed incoming barges to the foot of a wet stone incline. Using heavy ropes attached to massive human- or ox-powered capstans, workers dragged fully laden, multi-ton vessels directly up the slippery stone slope and over the crest into the higher body of water.
To lower boats, crew members let them slide down the lubricated incline, relying on ropes to prevent catastrophic crashes. Mud, clay, and water were smeared across the stones to reduce friction, turning boat transit into a high-stakes slip-and-slide. While pound locks eventually dominated world engineering, Haoba remained vital along specific sections of the Grand Canal for centuries because they consumed zero water—a critical advantage in arid regions or during seasonal droughts where opening a lock gate meant wasting millions of gallons of precious canal water.
It was loud, chaotic, and brutal on boat hulls, but the Haoba kept China's massive imperial trade network moving for centuries.