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Rowan Flad: 'I think salt production and trade did drive a lot of communication through this area.' (Staff photo Stephanie Mitchell/Harvard News Office)

Salt manufacturing is regarded as an important step in the development of complex societies because its trade not only spurred economic activity, it also encouraged communication along trade routes, prompted ethnic diversification in cooking, and opened new regions to settlement.

Archaeologists found evidence of large-scale salt production dating to the first millennium B.C. at a site called Zhongba, on the Yangtze River northeast of Chongquing. The site, upstream of the enormous Three Gorges Dam project, flooded in 2004 after excavation was complete and is now under the waters of the dam's manmade lake.

"It's very satisfying to have contributed to the work going on there," said Rowan Flad, assistant professor of anthropology at Harvard who was the lead author of a paper detailing the research. "It's an important area where a lot of evidence is now lost, or at least very hard to access."

Flad said the project not only uncovered new evidence of early Chinese salt production, but also pioneered new chemical methods through which researchers can confirm a site has been used to produce salt. Because salt so easily dissolves and washes away, confirmation of salt production at a site where it is suspected is difficult, Flad said. These chemical methods can help archaeologists further explore sites where salt production has been identified through pottery remains and other archeological evidence.

Flad's research was conducted along with colleagues from the University of Science and Technology of China, the National Taiwan University, the University of California, Los Angeles, the Sichuan Provincial Institute of Archaeology, and Peking University. It was published in the Aug. 30 issue of the Proceedings of the National Academy of Sciences.

Though far from the ocean, Zhongba is located in a region that is well known for its salt production. The area is believed to have been the site of an ancient sea that, when it dried up, left enormous deposits of subterranean salt that mingles with ground water and comes to the surface as a briny solution.

The Zhongba dig, begun in 1999, found a variety of evidence for large-scale salt production, including oval pits lined with clay similar to those found in salt production sites in Mexico and Africa, large vats whose design is similar to vats used in Japan to boil water to extract salt, and huge numbers of smaller cups thought to serve as molds to dry wet salt into bricks for transport and storage.

In addition to the more traditional archeological evidence, researchers analyzed the chemical composition of the site's soils and found trace elements from the local briny water - mainly calcium and magnesium - that were not present in soils from outside the site itself. They also found chemical residues in round-bottomed pottery at Zhongba that had similar characteristics to that found in 2,000-year-old salt boiling pans from Sichuan.

Finally, they also found salt itself, sodium chloride, in the pottery.

"It's an important step in understanding the economics of the region," Flad said.

The scale of the operation at Zhongba indicates that salt production probably existed at the site well before the date confirmed by researchers. Some objects found there dated more than a thousand years earlier, late in the third millennium B.C.

Salt's importance to early humans stems from our physiological need for the compound, Flad said. Salt became an important dietary addition with the rise of agriculture 10,000 years ago, when diets began to shift toward plant-based foods and away from saltier wild-caught meats, particularly fish.

Humans' taste for salt - familiar even today - outstripped our biological need for the substance, however, making it greatly desired and an early object of commerce. Salt use patterns quickly became ingrained in culture, further driving trade.

The salt trade would have been particularly important for the area around Zhongba, Flad said, because it was located far from population centers, on wild rivers whose navigation was made treacherous by rapids.

"I think salt production and trade did drive a lot of communication through this area, which was not otherwise easily traversed," Flad said.

alvin_powell@harvard.edu

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