Salt was dug from Sahara mines in large pieces of about 90 kilograms apiece, two of which could be carried by a camel. When the caravan reached Timbuktu, the salt was transferred to canoes and carried to Djenne. There it was divided into portions small enough for a man to carry one piece on his head. These porters traveled by foot in large groups, carrying their merchandise south for long distances. When they reached their destination they piled the salt in rows and then left the site to a spot a half-day's journey distant. While they were away another group of traders placed a quantity of gold by the piles and then left. Then the salt traders returned. If they were pleased with the amount of gold, they took it and left. If they wanted more gold they left the...