Ancient network of aqueducts provided salt for Silk Road trade during a time of worldwide flooding

Thousands of miles of ancient, man-made aqueducts were once vital to the salt trade of the Silk Road.

These elaborate systems were vital to the salt trade when worldwide coastal flooding rendered many sea salt basins useless, according to chemical engineering expert David Bloch.

Bloch, who presented his research at the 2018 World Salt Symposium in Park City, Utah, on June 20, said the 3,000-year-old aqueducts were utilized for irrigation and the production of purified salt.

“The engineering and architecture rivals that of the Great Pyramid of Giza or the Great Wall of China,” Bloch said according to the Salt Institute, a North American non-profit organization.

The irrigation channels, known as "Qanat" in Persia and "Karez" in Afghanistan and Central Asia, were able to carry water long distances by sloping deep underground, according to Bloch's abstract.

"There is hardly one central Asian community which does not get its water supply from Qanat aqueducts," Bloch said in an email.

The aqueducts used gravity alone to transport ground water into lower elevation areas via a vertical shaft, which prevented evaporation in arid climates.

It was critical that the amount of flood water was accurately controlled to avoid erosion of the flat basin.

According to Bloch, some tunnels stretch for more than 30 miles, or 50 kilometers, underground. In addition, more than 150,000 sweet water distribution systems comprise more than 120,000 miles of tunnels.

“The ancient Qanat-Karez provided surge flooding for short periods to desalinate the soil of the Sabkha basin,” Bloch said.

The leached salt formed a microbial, layered crust, allowing for the production of purified salt along the Middle Eastern section of the Silk Road.

Through a series of boreholes (a deep, narrow hole) and calculated timing, ancient people managed to control flood waters and facilitate the purification process by using leather bucket and opening and closing the apertures of the boreholes.

While its name derives from the profitable silk trade, the ancient Silk Road network of trading routes, spanning land and sea, also supported a lucrative salt trade with many coastal sea salt basins located in the Middle East and Central Asia.

The Silk Road was founded by the Han Dynasty in 130 B.C. and served not only as a vital trading network to the West until 1453 A.D. but also contributed greatly to the culture and history of civilizations across the Eurasian continent, which remain today.

Most of Europe's salt came from the Middle East during this time, relying heavily on sea salt basins for the commodity.

However, when worldwide coastal flooding rendered the sea salt evaporation basins of the Mediterranean Sea and China coastlines useless, the precious commodity ran short on supply.

"As a result of the considerable rise of the ocean [global] sea levels between the years 200 BCE and 300 CE, coastal evaporation pan, sodium-chloride salt was almost impossible to produce on an industrial scale, both in coastal China and Europe," Bloch wrote.

The exact cause of the global changes in sea level are still being debated by scientists, but the surge flooding needed for the aqueducts can be attributed to rainy winter seasons and hot summers.

"The salt industry is really the only witness to a similar rise between 200 BC and the 600 AD Islamic revolution, since the [Mediterranean] tide is only 20 inches, which was needed to fill the pans."

"The need to replace this lack of supply meant that much of the salt could only come from known inland sources such as rock mines, brine wells and saline lakes."

As a result, the Qanat Karez systems became essential components of the salt trade from 200 BCE to 300 CE, according to Bloch.

The desalinated soil was likely essential for production of layered salt slabs rather than for domestic or agricultural needs, Bloch said.

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