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Download What's instantly noticeable about the Forbidden City, which served as the home of emperors and their households for almost 500 years since the 15th century, are the enormous white stone 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 the world did they ever move this rock here?'" said Thomas Stone of the department of mechanical and aerospace engineering at Princeton University, as quoted by Nature magazine. Stone is part of a three-person team that recently discovered how. In a report published on Tuesday in the Proceedings of the National Academy of Sciences, they revealed that Chinese architects hauled the rocks from quarries in Fangshan, located 70 kilometers south of downtown Beijing, on wooden sledges along ice roads. Li Jiang, an expert in mechanical engineering from the University of Science and Technology Beijing and a member of the team that performed the study, found ancient Chinese documents describing how people transported a 120-metric-ton rock to repair three major halls in the Forbidden City in 1557. The ancient document, Lianggong Dingjian Ji, which translates as "the reconstruction record of two palaces", detailed how workers created man-made ice paths to transport the stone. The process was methodical: every half kilometer, wells were dug to obtain water, which was then poured onto a road and allowed to freeze to reduce the friction between the sledges and the road. | 
