Salt (sodium chloride or NaCl) has a fairly unobtrusive appearance in our modern society. But its low cost and ready availability today hides a historical importance to many if not most civilizations in the past. Salt was a crucial component of many complex societies, and many ancient battles can be attributed to the fight over control of salt sources.
Why Make Salt?
Salt, a moderate amount of it anyway, is essential for human life: its presence in the human body maintains the balance of fluids that carry nutrients and oxygen from the digestive system to the other parts of the body. Its chemistry controls our taste, smell and touch; it enables the transmission of nerve impulses from the brain; and it preserves the acid / base balance in the body as well. A long string of scientific studies shows that an excessive intake of salt is tied to high blood pressure and concomitant health issues, but people still crave it. None of this is what drove our ancestors to gain and fight for secure access to salt.
The primary attraction of salt in history and prehistory is its use as a preservative. The application of salt to organic material absorbs moisture, inhibiting the growth of bacteria and mold. That fact allowed societies to mass produce food and store it for lean times--a crucial piece of social engineering that made long-term survival through winters and droughts a possibility.
Salt is also used to tan leather and in dying cloth; and it was also used in many societies to preserve human remains after death--the most famous example is natron, a geological salt used by the Egyptians to mummify their pharaohs.
Salt Making as a Process
The two main methods of salt production are mining and extracting. Societies which rose near a body of saline water, particularly near the coastlines of any of our oceans, could extract salt from seawater or salt-enriched plants by the application of heat or exposure to the sun. Inland societies sought and fought for the right to mine geologically ancient salt deposits. Alternatively, they could establish trade networks or capture and rule over the salt-producing areas of the coasts or inland salt sources.
We don't really know exactly when active salt production from sea water began. A good bet though, is that salt production on a large scale could not have happened prior to the invention of ceramics (~15,000 years ago).
Salt extraction followed a standard procedure, no matter where or when the process was completed. Brine was collected and poured into large coarse ceramic containers; the containers were then placed over fires. The brine would have been boiled down to form a soft paste, or simply been allowed to concentrate and then be transferred to small pots which were then set aside to evaporate and cool. Once salt crystallization had occurred, the small pots were broken apart to obtain a hard, nearly weightless, easily transportable cake.
Ceramic pots used for making salt are remarkably similar, with nearly identical pot forms used in salt production sites throughout the world. Also similar across the world is the archaeological evidence left by salt production: ash, structural remains and briquetage middens. Briquetage is the word for the midden deposits created by the breakage of massive numbers of ceramic pots.
In coastal areas, salt production from seawater likely began as a craft specialization, with households producing their own salt, and, perhaps to trade after the producer's essential needs were met, or the support of elites allowed. A typical household-level production site has been identified at the Sigatoka Sand Dunes in Fiji. Trade from larger, more complex salt production activities dates at least to the Neolithic period of about 4500 years ago, at sites such as the Beaker period Molino Sanchón II, in Spain (~2000-2500 cal BC) and the Longshan and Shang dynasty Zhongba site in China (2500-1800 BC).
Also see: Salt is Ancient Mesoamerica
A Few Salt Production Sites
Sources
Burley DV, Tache K, Purser M, and Balenaivalu RJ. 2011. An archaeology of salt production in Fiji. Antiquity 85(327):187-200.
Flad RK, Xiaohong W, Von Falkenhausen L, Shuicheng L, Zhibin S, and Chen P. 2009. Radiocarbon Dates and Technological Change in Salt Production at the Site of Zhongba in the Three Gorges, China. Asian Perspectives 48(1):149-181.
Flad R, Zhu J, Wang C, Chen P, von Falkenhausen L, Sun Z, and Li S. 2005. Archaeological and chemical evidence for early salt production in China. Proceedings of the National Academy of Sciences 102(35):12618-12622.
Guerra-Doce E, Delibes de Castro G, Abarquero-Moras FJ, del Val-Recio JM, and Palomino-Lázaro ÃL. 2011. The Beaker salt production centre of Molino Sanchón II, Zamora, Spain. Antiquity 85(329):805-818.
MacGregor GA, and Sever PS. 1996. Saltâ€"overwhelming evidence but still no action: can a consensus be reached with the food industry? BMJ 312(7041):1287-1289.
Megaw V, Morgan G, and Stollner T. 2000. Ancient salt mining in Austria. Antiquity 74:17-18.
Proske U, Heslop D, and Hanebuth TJJ. 2009. Salt production in pre-Funan Vietnam: archaeomagnetic reorientation of briquetage fragments. Journal of Archaeological Science 36(1):84-89.
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