At an ancient Chinese settlement straddling a river, scientists have uncovered what they regard as the earliest strong archaeological evidence of salt making, dating to 4,000 or so years ago.
This discovery highlights salt’s central role in promoting the development of early states and empires, contend Rowan Flad of Harvard University and his colleagues. Large-scale salt production at critical locations in China led to extensive trading of the seasoning and of salted foods, they propose. Salt became crucial for provisioning armies of expanding Chinese states by 221 B.C., according to historical accounts.
In the Aug. 30 Proceedings of the National Academy of Sciences, Flad’s group describes findings from the ruins of Zhongba, a settlement along central China’s salty Ganjing River. “In southern China, salt from Zhongba was a vital component in the complex process of state formation,” the scientists conclude.
Each of three periods of activity at Zhongba yielded remnants of vessels used in a process of boiling river water to produce loose salt or salt cakes. From the earliest period, dated at 2000 B.C. to 1750 B.C., the team found large, pointed-bottom vats that were used either to store or to boil salt water.
In the second period, which ranged from 1630 B.C. to 1210 B.C., many small, pointed-bottom cups appeared. The cups served as molds for salt cones to be traded, the researchers suggest.
Small, round-bottomed jars dominate remains from the third period, which extended from 1100 B.C. to 200 B.C. Similar vessels are still used today in various parts of the world to boil salt water and to make salt cakes.
Other evidence has confirmed salt making, the scientists report. For instance, chemical analyses of soil from rectangular pits at Zhongba and of river water at the site yielded comparably high concentrations of calcium and magnesium. This finding suggests that river water was stored in the pits.
Chemical residue on the inside of the round-bottomed jars appears to be calcium oxide, a substance known to form during the salt-making process. Finally, a scanning electron microscope revealed traces of salt crystals inside many Zhongba vessels.
These methods of certifying ancient salt production represent “an important advance,” remarks Yale University archaeologist Frank Hole. Such techniques should now be applied at 6,000-year-old sites in the Middle East where archaeologists suspect salt making, he says.
Archaeologist Li Liu of La Trobe University in Melbourne, Australia, also welcomes the new report. However, she and her colleague, Xingcan Chen of the Chinese Academy of Social Sciences in Beijing, say that it’s unclear how Zhongba salt making related to Chinese civilization’s rise.
The earliest states arose in northern China roughly 4,000 years ago and had no contacts with Zhongba, Liu and Chen say. Earlier this year, they reported in a Chinese journal that 39 northern Chinese sites dating to Zhongba’s heyday contain pottery and other remains of salt-making operations, although chemical and microscopic analyses have yet to be conducted.
Correction: This article correctly stated that archaeologists Li Liu and Xingcan Chen reported on 39 northern Chinese sites containing remains of salt-making operations, but they shouldn’t have been credited with those findings, which were by other Chinese archaeologists earlier this year.