Lingqu is actually made up of two canals. What was built during Emperor Qin Shihuang's (259 BC-210 BC) time was the South Canal, and only the first 10 km were dug by human hands - the rest flows into the original Lingshui River. But these 10 km were so punishing that the first two engineers were executed by the habitually despotic ruler Qin.

For one thing, Xiangjiang River on the East has more water but is lower by 4.34 meters at the closest lateral points. To solve the uneven altitude problem, the canal has to start higher in Xiangjiang. For a long stretch, it runs parallel with Xiangjiang but is much higher. It drops a total of 30 meters in its 33.15-km course.

The North Canal was built by Ma Yuan, the general whose horse warned him of impending danger. Stretching only 3.25 km, it was designed to divert water and facilitate navigation by lengthening the original 1.5 km and thus smoothing out a 5.6-meter drop - the equivalent of a wheelchair access ramp built next to a flight of stairs. The technology of the time could not handle the lifting of boats over dams.

Likewise, the division of water flows was made possible by a 3-meter levee that is narrow at the front and gains width downstream. In the shape of a plowshare mouth, it routes 30 percent of the water to the South Canal and 70 percent to the North.

A creation of a Tang Dynasty magistrate in AD 825, this water-splitter has pine wood as a foundation and stone slabs surrounding gravel and silt. Over the centuries, this "plowshare" has been pushed downstream by some 80 meters.

Another Tang official perfected the locks along the canal in AD 868. Locks were constructed at shallow places, with stone frames on both sides and 5-6 meters for the lock or the passage of boats. They were used to dam water for upstream. The number of locks was increased and the material strengthened, albeit still mostly wood. They were substituted with stone slabs in later eras.

Like a lot of primitive inventions, Lingqu was the result of trial and error. Even local mythologies have incorporated and commemorated the hardships and sacrifices.

Legend has it that the evil river god was offended when the canal opened after the first engineer worked on it for 333 days. Annoyed by the sounds of water, he opened his big mouth and bit off the embankment. The engineer was beheaded as a result.

By the time the third engineer took his place, a peripatetic immortal happened to come by and blessed him with magical powers. When the river god was to wreak havoc as usual, a dark cloud emerged. Amid hailstorms and flying stones, a gigantic rock crushed the river god, forever confining him.

Now, the 7-meter-high-by-10-meter-wide black rock is emblazoned with all kinds of inscriptions. But nobody - not even modern science - can tell its origin. Just like Stonehenge, it sits in solitude but sandwiched by two rivers - one wrought by nature and the other carved by human ingenuity.