London: Researchers have revealed that the huge stones that make up parts of China`s Forbidden City were transported along artificial ice paths lubricated with water.
That`s despite the fact that wheeled vehicles had been developed 3,000 years earlier.
The colossal city was built in the 15th Century by workers at the start of the Ming dynasty.
The team said that wood-on-ice sliding was more reliable than using wheels, the BBC reported.
Using sledges on ice was much more expensive and needed more workers but it was deemed a safer method than mule-powered transport.
Howard Stone, professor of mechanical and aerospace engineering at Princeton University, said that on his first tour of the Forbidden City, he and colleagues were curious about how some of the huge stones had been transported.
When the team translated a 500-year-old document from the historical record, they found a mention of huge stone carvings transported on ice.
They then made calculations looking at the friction of ice to see how plausible it would be to drag such large rocks over the short time period in winter, when it was cold enough to do so.
Prof Stone said several hundred workers would have been needed to transport stones ranging from 100-300 tonnes.
The study is published in the PNAS journal.