Chinese used ice-path sleds to move Forbidden City’s stones

Icy routes were laid for sliding super-size stones.

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While visiting and enjoying the architecture of the Forbidden City in China, three researchers wondered how large rocks weighing many hundreds of tons were transported to the site more than 500 years ago. A relaxing holiday became a science project, and in a paper just published, the researchers reveal calculations showing that the most likely means of achieving this feat was by using wooden sleds on artificial ice paths.

Built in the early 15th century, the Forbidden City consists of an imperial palace and nearly a thousand buildings. It served as the figurative center of China’s capital city. During the researchers' visit, Howard Stone, professor of mechanical and aerospace engineering at Princeton University, saw a sign that mentioned the use of an artificial ice path to transport the enormous stones used in the city.

However, a look at the history of technology in China revealed that wheels existed in China since the 4th century BC. Why, then, would there still be a need to use human-pulled sleds? “That is when we began to investigate and calculate,” said Stone.