China city materials were moved using ice

Imperial guardian lions at the Forbidden City. Image Credit: CC BY-SA 3.0 Allen Timothy Chang

China's 15th century Forbidden City was built by moving blocks along artificial paths made from ice.

Constructed at the beginning of the Ming Dynasty, the city was thought to have been built from materials transported using traditional wheeled carts, but now a new research effort has revealed that the ancient Chinese workers may have used ice instead.

"Most scholarly work indicates that the Chinese had the wheel in 1500 BC and the conclusion from that was they didn't have any need for sledges dragged by man," said Prof Howard Stone. "So our suggestion is somehow that they didn't recognise the use of the artificial ice paths to drag these large rock carvings."

To corroborate this idea, the team calculated the feasibility of dragging huge stone blocks 43 miles across an ice-covered surface. "If you look at the frictional characteristics of ice for the rocks of this size, we estimate that 300 people were needed for this kind of dragging," said Prof Stone.

The workers would have needed to build wells every few kilometers from which they would haul the water before spreading it on the road. As the water turned to ice, the low friction surface would have been ideal for helping to move the giant stones along.