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Nov 23 2013

How do you move a huge stone?

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.

12 comments

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  1. 1
    Matt G

    Get crucified.

  2. 2
    Rob Grigjanis

    Anyone who has done much running in wintery conditions can testify to the amazingly small coefficient of static friction between shoes and ice with a thin layer of water on it. You’re in midair before you can even blink.

    A recent program on the Moai of Easter Island showed an interesting take on the legend that the statues walked to their resting places.

    http://video.nationalgeographic.com/video/specials/nat-geo-live-specials/hunt-lipo-animation-bonus-nglive/

  3. 3
    wtfwhateverd00d

    So with the cold icy conditions, what was footwear like at the time?

    The followon calculation were how many men were required to supply a constant 50 men doing the work?

  4. 4
    wtfwhateverd00d

    The birth of our health care system was Henry Kaiser organizing healthcare for his workers and their families in an attempt to make the workers more productive. As a Kaiser Kid myself, I thought his system worked pretty well. We got care and it was mostly free, though there were long lines at the pharmacy.

    And then others came in and saw how to take a working system and corrupt it….

  5. 5
    wtfwhateverd00d

    And of course, health care should not rely on employers. People must be free to work where they want without relaying on employer provided healthcare.

  6. 6
    Andrew G.

    The largest rock ever moved overland by human labour (no animals or powered machinery) weighed a staggering (estimated) 1,500 tonnes (of which about 250 tonnes were carved off). It is known as the Thunder Stone, and now forms the base of the statue of the Bronze Horseman in St. Petersburg. It took nearly two years to move, from 1768 to 1770.

    The Broken Menhir of Er-Grah in Brittany, which weighed around 300 tonnes, was erected around 4700 BC (having been moved several kilometers from where it was quarried). (It probably broke around 4000 BC.) This is the largest known Neolithic monolith.

  7. 7
    Pierce R. Butler

    … 50 people pulling together …

    Or five people, each leading two oxen.

  8. 8
    Dalillama, Schmott Guy

    It took only 9 months of actual work, though, they just occurred over several consecutive winters. They had to move it when the ground was frozen. The sledge was run on brass ball bearings and hauled via capstan; it took only about 70 men actually pulling, or rather working the huge capstans that did the pulling; the effort certainly used machinery, although it was human powered.
    Of course, knowing this allows us to infer things about the methods that might have been used by other megalithic constructors. Ancient Egypt is known to have used pulley-operated cranes at the docks, and classical China was also more than capable of assembling pulleys, capstans, etc, although it’s also known that many Imperial Chinese governments were happy to just throw slave labor at something until it got done instead of bothering with a technical fix. Egypt, OTOH, certainly had loads of slaves, but as I understand it the current archaeological consensus is that the pyramids were mostly built by farmers looking for wage work in the off season. I’ve also seen a quite convincing (to me anyway) explanation of how counterweights and sledges could have been used to get the assembly of the pyramids done with considerably less labor than might be assumed. The builders of megaliths like Stonehenge aren’t known to have had as much in the way of cranes and pulleys, but then we also have no real idea how long it actually took them to assemble the thing either. .

  9. 9
    thewhollynone

    Such a monumental construction was a vanity project for the elite classes, yes, but also a make-work project for the lower classes, and a means of redistributing some of the wealth in the form of beer, cereal, and a very small amount of currency. The males worked on the constructions and the females ran businesses supplying the physical needs of the workers. Strong young men must be kept busy exercising their muscles in some socially acceptable way or else they will fight among themselves and cause inordinate amounts of trouble; in our modern culture we have football for that.

    I visited the Forbidden City in 1999, and it is indeed a fabulous thing to see; I also visited Machu Picchu, and that takes one’s breath away, literally. Some of the ancient temples in the Mediterranean area are also wonders just now being unearthed by archaeologists. I wish those young men in Syria and Turkey and Palestine would stop fighting among themselves so that it would be safe for me to visit those sites where agricultural communities were invented. I would also like to see for myself the enormous stones which composed the walls of ancient Troy before I get entirely too old to travel. I keep hoping that some elite someone will come up with a make-work project to put all those middle-eastern muscles to work in some socially acceptable way.

  10. 10
    Marcus Ranum

    Were any of the wonders of the ancient world NOT built with slave labor?
    I suppose the alternative for conquered people was death. Warehousing people is a fairly modern phenomenon.

    The ice theory sounds ok but appears to make assumptions about how level, smooth, and impermeable the roads were. I’ve played on Roman roads and can’t speak for Chinese roads but we are not talking about poured concrete surfaces… (Also, modern roads don’t like having 60-tonne main battle tanks driving on them)

  11. 11
    Marcus Ranum

    I keep hoping that some elite someone will come up with a make-work project to put all those middle-eastern muscles to work in some socially acceptable way.

    Yeah, ‘cuz fighting for freedom is so damned rude.

  12. 12
    Jared A

    “Were any of the wonders of the ancient world NOT built with slave labor?”

    Probably the egyptian pyramids were not.

    http://en.wikipedia.org/wiki/Egyptian_pyramid_construction_techniques

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