In 1352 the great Moroccan traveler Ibn Battuta arrived after a punishing 25-day crossing from Sijilmasa, bound for the Mali Empire. He was not impressed. There were no trees, he wrote, nothing but sand and the mines. The water was brackish, the village full of flies. Salt was dug from the ground in thick slabs, two loaded onto each camel and carried south to Oualata to be sold. And yet, for all its meanness, the place was 'awash in Malian gold.' That contradiction is the whole story of Taghaza: a miserable village that the rest of West Africa could not do without, because the human body needs salt and the savanna could not provide it.

The economics were almost surreal. Salt was so scarce in the Sudan, the lands south of the desert, that people cut it into pieces and used it as currency, buying and selling with chunks of it as others did with coins. A load that fetched eight to ten gold mithqals at Oualata could sell for twenty, thirty, even forty in the Malian capital - its value multiplying with every brutal kilometer it was hauled. Caravans came once a year to carry it off. By 1375 Taghaza was famous enough to appear on the Catalan Atlas in Europe, a tiny marker on the trade route that bound Sijilmasa to Timbuktu and, beyond it, the goldfields that made empires rich.

None of this wealth belonged to the people who produced it. Nobody actually lived in Taghaza, the chroniclers noted, except the enslaved miners of the Masufa, a Berber group, who hacked the salt from the ground in a place 20 days' journey from the nearest food. They survived on dates and millet hauled in from Sijilmasa and the Sudan, and camel meat. Leo Africanus, visiting around 1510, observed that a caravan arriving late could mean starvation for the men left waiting. They built their shelters from the only material to hand - the salt itself - and labored in heat that today ranks among the most extreme on the planet. The gold that flowed through their hands was never theirs; the work, and the risk of dying of hunger between deliveries, was.

Whoever controlled Taghaza controlled a fortune, and so the mines became a chess piece between empires. They passed under the Songhai, whose capital at Gao lay 970 kilometers across the sand. In the 16th century Morocco's Saadian sultans pressed again and again to seize them - sometimes by demand, sometimes by raid. When the Songhai answered one demand with a defiant gift of 47 kilograms of gold and later with outright refusal, the Saadian sultan Ahmad al-Mansur sent an army of 4,000 mercenaries across the Sahara under the Spaniard Judar Pasha. The Songhai were crushed at the Battle of Tondibi in 1591, and their empire collapsed. Taghaza, fittingly, was the spark.

Victory ruined the prize. After the conquest Taghaza was abandoned, its trade shifting 150 kilometers southeast to Taoudenni, which lay closer to Timbuktu and so cost less to reach. But the town did not entirely vanish. When the French explorer Rene Caillie passed in 1828, traveling with a caravan of 1,400 camels, he could still see the ruins of houses built of salt brick standing in the waste. They are there yet - two settlements on either side of the old salt flat, their walls aligned against the prevailing wind, the mosque still distinguishable among them. A ghost town made of the very thing that, for a few centuries, was worth its weight in gold.