What's instantly noticeable about the Forbidden City, which served as the home of emperorsand their households for almost 500 years since the 15th century, are the enormous whitestone foundations supporting the historical site's 980 wooden buildings.
"You go to the Forbidden City and see these massive rocks and you ask yourself: 'How in theworld did they ever move this rock here?'" said Thomas Stone of the department of mechanicaland aerospace engineering at Princeton University, as quoted by Nature magazine.
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Tourists visit the Forbidden City, Aug 19, 2013. [Photo by Yan Daming/Asianewsphoto]
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Stone is part of a three-person team that recently discovered how. In a report published onTuesday in the Proceedings of the National Academy of Sciences, they revealed that Chinesearchitects hauled the rocks from quarries in Fangshan, located 70 kilometers south ofdowntown Beijing, on wooden sledges along ice roads.
Li Jiang, an expert in mechanical engineering from the University of Science and TechnologyBeijing and a member of the team that performed the study, found ancient Chinese documentsdescribing how people transported a 120-metric-ton rock to repair three major halls in theForbidden City in 1557.
The ancient document, Lianggong Dingjian Ji, which translates as "the reconstruction record oftwo palaces", detailed how workers created man-made ice paths to transport the stone. Theprocess was methodical: every half kilometer, wells were dug to obtain water, which was thenpoured onto a road and allowed to freeze to reduce the friction between the sledges and theroad.
"The 49-cubic-meter rock was hauled to Beijing in four weeks. That is an average speed ofabout eight centimeters per second," Li said.
The scientists were amazed that ancient Chinese builders continued to use the slow, laboriousmethod well into the 16th century, even after wheeled vehicles had been present in China formore than 3,000 years.
"When we talk about hauling in a mechanical engineering context, we often think of ancientEgyptians and Assyrians, but we do not usually refer to ancient China," Li said.
In science history publications, such as Duncan Dowson's classic History of Tribology, "thehaulage of colossal statues by masses of men does not appear in any kind of ancient Chineserepresentation", because wheels with spokes appeared in China at about 1500 BC.
The researchers found that the ancient Chinese combination of ice paths and sledges were thesafest and most efficient way to transport massive objects.
"Ancient documents until the late 16th century show that wheeled vehicles could carry amaximum load of 95 tons. So workers had to find other methods to ship the multi-ton rocks," Lisaid.
Sledges were also used to keep the expensive large stones from being damaged.
Studies comparing the ancient Chinese technique of transporting stone with methods fromother ancient civilizations show it is more efficient to drag the sledges rather than to usewooden rollers, as the Assyrians did.
Stone said the team's calculations show that dragging the 120-ton rock with a sledge overground that was not frozen with ice would have required a labor force of more than 1,500people. On ice or wet wooden rails, on the other hand, it would have required 330 men. Theancient Chinese practice of hauling stone along an ice road lubricated by water would haveneeded fewer than 50 men.
chengyingqi@chinadaily.com.cn
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