The modern engineers believe that pulling sledges over ice paths lubricated with water, was a more efficient option that rolling the stones over logs.|
In the study published in journal Proceedings of the National Academy of Sciences, they said the coefficient (a quantitative expression of a specific property of matter) of friction for logs rolling along a path is 0.2 to 0.4, while using the water-and-ice-sliding method, has a coefficient of just 0.02.
The experts also said that sliding sledges is easier than using logs as it is easier to make a smooth ice road than to have to make a level one of planks and manoeuvre the log rollers as well as the huge chunk of stone.
Wheeled vehicles of the time would not have been able to support the weight of the large stones, according to the engineers, who think that the maximum weight carts would have been able to pull would have been 95 tonnes.
They said that ice roads and men were also more reliable than mules and carts, especially as the architects of the Forbidden City were reportedly worried about keeping the expensive stone safe.
The team of engineers said winter in Beijing 600 years ago was cold enough to keep roads frozen, which was useful for transporting stones. Here, Chinese paramilitary police officers shovel snow off a walkway in front of an old building in the Chinese capital