Ice aided construction of Forbidden City

Workers slid heavy stones on paths covered with liquid and frozen water

Artificial ice paths probably helped Chinese workers slide heavy stone, such as this 300-ton marble carving, into the Forbidden City in Beijing, China, when the site was built in the 15th and 16th centuries.

Courtesy of Chui Hu

The heavy stones of the Forbidden City were probably slid into Beijing on ice paths.

Chinese workers could have used wheeled carts to move the 100-ton stones. But the laborers probably preferred sliding the chunks across ice because wheeled carts could hit bumps in the road and cause damage to the expensive stone, researchers report November 4 in the Proceedings of the National Academy of Sciences.

The researchers translated a 500-year-old document describing how Chinese workers slid a 120-ton stone on water-lubricated wood along an ice path into Beijing in the winter of 1557 A.D.

Using the historical account, the scientists calculated that workers could slide the load at about eight centimeters per second, fast enough to move it forward before the water froze. The method would require only 50 men, compared to the 1,500 needed to pull the same load across the ground, the team suggests.

photo of Ashley Yeager

Ashley Yeager is the associate news editor at Science News. She has worked at The Scientist, the Simons Foundation, Duke University and the W.M. Keck Observatory, and was the web producer for Science News from 2013 to 2015. She has a bachelor’s degree in journalism from the University of Tennessee, Knoxville, and a master’s degree in science writing from MIT.

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