Why Would Anyone Cross a Desert for Salt? A Necessity That Grew in Few Places

The trade exists because of an awkward combination of properties. People and livestock must have salt, so demand is universal and inelastic. It occurs only where seawater can be evaporated, where rock deposits exist or where salt springs emerge, so supply is concentrated in specific places. It is heavy relative to its value, so transporting it is expensive, and it was nonetheless transported enormous distances because the alternative was doing without. Before refrigeration it was also the principal means of preserving food, which multiplied demand well beyond dietary need, since a community that could not preserve a harvest or a catch could not survive a winter or trade its produce at any distance.

Production concentrated in a small number of kinds of place:

• •Coastal evaporation pans, worked wherever the climate allowed
• •Rock salt mines, some of which have operated for over seven hundred years
• •Inland salt springs, boiled down using enormous quantities of fuel
• •Desert salt pans, cut into slabs and carried out by caravan
• •Salt lakes, harvested seasonally
• •Burning of salt-rich plants, used where nothing better was available

Several of these trades were substantial enough to shape political geography. Caravans crossed the Sahara carrying slabs cut at desert mines southwards and returning with gold, and the states of the West African Sahel grew wealthy taxing that traffic, with salt exchanged against gold at rates that astonished visiting writers. Roads across the Alps carried salt from Salzburg and from Alpine mines into central Europe, and several towns owe their existence and their names to it. Ethiopian caravans carried slabs from the Danakil depression, a trade that continued into recent years. Chinese salt administration was among the oldest and most sophisticated state monopolies anywhere, dating to well before the common era.

The importance of the commodity is fossilised in ordinary language in several places. The English word salary derives from a Latin term connected with salt, and the popular claim that Roman soldiers were paid in it is a simplification that ancient sources do not clearly support, with the more defensible version being an allowance connected with its purchase. The phrase about being worth one's salt derives from the same association. Place names across Europe record production, with elements meaning salt appearing in the names of Salzburg, Halle, Hallstatt, Nantwich, Droitwich and many others, and those towns can frequently be identified as production centres from the name alone. Roads and streets named for it mark the routes along which it moved.

A commodity everybody must buy, produced in few places and passing through identifiable routes, is an almost perfect subject for taxation, and governments recognised that consistently. Monopolies and duties on salt were among the most important revenue sources in China, France, India and elsewhere for centuries. They were also among the most resented, since they fall hardest on the poorest, and they generated large-scale smuggling, private armies of enforcement officers, and repeated revolt. The French version was abolished in the revolution and reinstated afterwards. The British monopoly in India, which made it illegal to produce salt from the sea, became the target of a mass civil disobedience campaign in 1930 that was chosen precisely because the injustice was so easy to explain.

Universal demand, concentrated supply and a low value relative to weight are exactly the conditions that produce long-distance trade, and preservation multiplied demand well beyond dietary need. Saharan caravans exchanged desert slabs for West African gold, and Alpine and Chinese trades were comparably significant. A commodity everybody must buy is ideal for taxation, which produced monopolies, smuggling, revolts and the Indian campaign of 1930.