In the Forbidden City, a city within the city of Beijing consisting of massive palaces and temples built in the 15th and 16th centuries, some of the stone slabs used in the construction weigh 100 tons or more. According to contemporary records they were quarried 70 kilometers away.
So the question that naturally arises, as with other giant ancient monuments like Stonehenge and the Pyramids, is how the stones were moved from the quarry area to the final location, since the wheeled vehicles they had at the time could not bear such heavy loads. Moving them on wooden rollers also would not work.
According to a report in Nature:
For one thing, Stone notes, using wooden rollers — imagine telegraph-pole–sized tree trunks as large bearings — is tricky on winding roads. The technique also requires a smooth, hard surface to prevent the rollers from becoming mired. Dragging a 112-tonne sledge over bare ground would require more than 1,500 men, Stone and his colleagues estimate. Pulling the same sled across bare ice or across wet, wooden rails would require at least 330 men.
According to the records, one of the stones in Beijing was moved over a road of ice in the surprisingly short time of 28 days in January, so scientists and engineers set about calculating how it could have been done with a reasonable number of people. It all hinges on the coefficient of friction between the sledge holding the stone and the road. A team of Chinese and American scientists have published a paper in the Proceedings of the National Academy of Sciences saying that it was possible if you placed the stone on a wooden sledge that moved over an iced road that was kept lubricated with a thin film of water to lower the friction.
The paper describes (citations omitted) how this might have been done.
Here we suggest that a lubricating film of water was created by directly pouring well water on the ice-covered ground to wet the contact surfaces during the movement of the sledge. As the sledge starts moving the water poured in front of the sledge would lubricate the sliding surface, as is illustrated in ancient Egyptian bas-reliefs. In addition, although the sledge slides on the ice surface at a low speed of 8 cm/s, the value of μ could still be as low as that in the high-speed regime with poured water, because when a film of water is present the coefficient of static friction is very small, ∼0.02, at a temperature close to but still below 0 °C.
Thus 50 people pulling together could move the stone 8 cm/s or about 16 feet per minute, just fast enough to get it done. In order to have the ready supply of water for lubrication, they dug wells every half a kilometer along the way.
On the one hand such monuments show incredible ingenuity. On the other, one has to think of the enormous human cost to construct what are essentially vanity projects for powerful rulers, likely using slave labor. We admire these monuments now because the mists of time hide the horrors that lie behind the construction.