On the edge of Timbuktu, in western Africa, where the city blends into the Sahara, a group of exhausted camels lie resting on the sand.

The caravan of beasts, some 30 in total, arrived in Timbuktu after a five-week trek through the Sahara. Most have carried four large discs of solidified salt each, a combined load of some 160 kg, the whole distance.

The journey has been an arduous one, both for the animals and for their human handlers, but the cargo, carried from a mine in the desert, is worth it. In days gone by salt here was as valuable as gold, and even today profit margins in the trade are over 100 percent.

The camels belong to Mohammed Bouge, whose family has been in the salt trade for generations. The 50-something camel drover has made countless trips between the mines and the city.

Daytime temperatures can reach 50 degrees, while the desert wind is also a force to contend with. "A caravan can consist of hundreds of animals. Sometimes we ride on top of the camels and sometimes we walk beside them."

The destination of the caravans is Taoudenni, a remote and inhospitable oasis some 700 km north of Timbuktu. The layers of underground salt deposits in the region are the remnants of dry lake beds.

On the outward trip, the caravans carry rice and millet for the workers in the mines. In Taoudemi, salt slabs are loaded on to camels' backs using thin hide straps though they are well-protected by cushioning sacks of straw strapped to their flanks.

"In Taoudenni each slab costs about 3.80 euros ($4.60)," Mohammed says. "In Timbuktu we can sell them for twice that."

From Timbuktu, traders ship the slabs to Mopti, at the confluence of the rivers Niger and Bani, a distance of 400 km or three days by boat.

Like Mohammed, Boubacar, another Arab tribesman sits on straw mats under a low canopy, waiting patiently for customers. His salt slabs are stacked behind him, bound together with leather straps.

Salt from the Sahara is highly valued in Ghana, in Burkina Faso and as far south as the Ivory Coast. "It tastes much better and is much healthier than sea salt," says he.

Because of the extreme climate in the region, salt is essential for the health of both livestock and humans. In countries with no direct access to the ocean, Sahara salt is also much cheaper than imported sea salt.

Boubacar spends most of the year not at the market, but mining for the mineral in Taoudenni. Half proud, half embarrassed he displays his hands, scarred in many places. "The work is very, very hard," he says. "But you can earn a lot."

The salt lies up to three metres under the surface and the workers dig it out by hand. "When you are injured, the salt burns into the wound," Boubacar says.

The Saharan salt is one of the reasons why the city of Timbuktu reached its legendary status during the 15th and 16th centuries.

The decline of the city began with the invasion of the Moroccans at the end of the 16th century. The city was looted, with many wealthy residents and intellectuals deported to Fez, now part of Morocco. Later, European ships landing on the west African coast made much of the caravan trade superfluous.

Today, Timbiktu struggles with an all-powerful desert that appears eager to reclaim its land. A fine coating of sand is spread over every lane and many walls are almost buried.

Only when the moon comes up and the city sleeps do the drovers turn towards the north.

"Camels do not like noise," says Mohammed, who, like his father and his grandafather, will keep making the long trek to Taoudenni and back, carrying precious salt across the desert.

--DPA