Chinese used ice-path sleds to move Forbidden City’s boulders

While visiting and enjoying the architecture of the Forbidden City in China, three researchers wondered how large rocks weighing many hundreds of tons were transported to the site more than 500 years ago. A relaxing holiday became a science project and, in a paper just published, they reveal calculations to show the most likely means of achieving this feat was by using wooden sleds on artificial ice paths.

Built in the early 15th century, the Forbidden City consists of an imperial palace and nearly a thousand buildings. It served as the figurative centre of China’s capital city. During the researchers’ visit, Howard Stone, professor of mechanical and aerospace engineering at Princeton University, saw a sign that mentioned the use of an artificial ice path to transport the enormous stones used in the city.

However, a look at the history of technology in China revealed that wheels existed in China since the 4th century BC. Why then would there still be a need to use man-drawn sleds? asked the researchers. Was it a better method? “That is when we began to investigate and calculate,” said Stone.

From quarry to site, about 70km. Howard Stone and Jiang Li

With the help of Jiang Li, a mechanical engineer at the University of Science and Technology Beijing who studies tribology (study of friction), they dug into the literature to find more details on the efforts involved in transporting these stones. One document said that a monolithic slab weighing 112 tonnes was moved over 70km to Beijing in 1557.

Chinese wheeled carriages would not have been able to transport such blocks, even with the technology of late 1500s. The other idea would be to use wooden rollers, but that would required creating a smooth road on tricky winding roads.

Calculations published in the Proceedings of the National Academy of Sciences reveal pulling such stones over bare ground at a rate mentioned in the historical text would require more than 1500 men. Even sliding the stone on bare ice would need 330 men. However, one solution from the researchers, which involved tobogganing the stones on wooden planks and lubricating the path with cold water, would only need 50 men for that load.

A weather analysis of the last 2000 years in China finds the average January temperature in Beijing in the 15th and 16th century was about –4°C, which would have been enough to create and maintain artificial ice paths. While historical records reveal that more than a million workers were involved in the construction, details about the construction activity are hard to find.

The Chinese were at the forefront of the study of friction at the time. Chariots preserved with the Terracotta Army, which is more than 2000 years old, showed they even used wheel bearings to reduce friction.

“It’s a wonderful story and a good historical analysis,” said Thomas Mathia, a tribologist at French National Scientific Research Centre. “But it’s just a hypothesis.”

Regardless of whether or not they are able to prove that tobogganing massive stones played a part in the construction of the Forbidden City, for Stone the pleasure was in following up the story. “Recognising the degrees of planning and implementation used more than 500 years ago for such a massive undertaking was humbling.”The Conversation

First published on The Conversation.

Image credit: inkelv1122

Computer simulations reveal war drove the rise of civilisations

According to British historian Arnold Toynbee, “History is just one damned thing after another.” Or is it? That is the question Peter Turchin of the University of Connecticut in Storrs tries to answer in a new study just published in the Proceedings of the National Academy of Sciences. He and his colleagues show history may be deterministic, at least to a certain extent. Their computer simulations show that warfare may have been the main driver behind the formation of empires, bureaucracies and religions.

Historians may be a bit leery about scientists making this sort of attempt, since history is driven by a complex set of of events, some of them seemingly one-time only. But Turchin thinks otherwise. Through an approach he calls cliodynamics (named after Clio, the Greek muse of history), he wants to unravel the past by testing hypotheses against data.

For his latest work, he joined with Thomas Currie, a lecturer in cultural evolution at the University of Exeter. In the new study, they use a computer simulation to model the largest societies in the years between 1500 BCE and 1500 CE.

Their model uses a map of Africa and Eurasia split up into cells that are 100 kilometres on each side. The properties of each cell are its natural landscape, height above sea level and the possibility of agriculture (which was the main driving force behind societies). The borders are seeded with military technology, starting with the use of horses. That technology then spreads as societies fight it out virtually. What emerges is the probability that each cell of land could or could not be occupied by civilisations as time progresses.

Red depict higher probability of existence of a civilisation and green lower. Thomas Currie

“Remarkably, when the results from the simulation are compared with real data from the past, the model predicts the rise of empires with 65% accuracy,” Currie said. If military technology is removed as a factor, the model’s accuracy falls to a mere 16%. “It seems warfare created intense pressure that drove these societies.”

Other researchers such as Jared Diamond and James Robinson have suggested, respectively, that agriculture and social institutions drove civilisations. They undoubtedly contributed, but Turchin and Currie argue that their results show that competition through warfare may have played a more important role.

Peter Richerson, emeritus professor at the University of California at Davis, studies cultural evolution and is impressed by cliodynamics. “It is early days yet, so the specific hypothesis tested here is liable to prove wrong or at least incomplete,” he said. “The model fails to predict the emergence of large empires in Central Asia. Something not in the current model is going on there.”

Currie agrees. “Our results are a good fit because of the broad scale. We are aware we are glossing over many complexities,” he said. Still, there is lots of potential value in building these models. The global database of historical events has many gaps. With efforts underway to grow these databases through all the information that historians, archaeologists and social scientists can find, the models are bound to get better.The Conversation

First published on The Conversation.

Image credit: kaptainkobold