The salt trade, already important in the Bronze Age, grew more and more important over time. By 252 BC, a Chinese governor named Li Bing also figured out how to mine salt. People dug deep pits down to where there were natural underground salt water pools, and forced the salty water out through bamboo pipes.
People in China generally didn’t sprinkle salt on their food the way you do. Instead, they mixed salt and soybeans to make soy sauce. They also used salt to make pickled vegetables – not just cucumbers, but all kinds of vegetables. That was the only way to keep them from rotting. The ancient Egyptians also used salt to pickle vegetables, especially olives. And the ancient Greeks and Romans used salt to make a fermented fish sauce called garum.
Because everyone needed salt, but only a few people could produce it, salt was something everybody bought. So governments began to tax it, to raise a lot of money. Both the Han Dynasty and the T’ang Dynasty, in China, got a lot of their money from the salt trade. As the Roman Empire expanded, the Romans took over the Celtic salt mines, and used that salt to help feed poor people in Rome, or to raise money (for example to pay for the Punic Wars).
When people began to use camels for trade caravans across the West Africa, about 1000 AD, merchants brought salt across the desert on the backs of the camels. Caravans of up to 40,000 camels carried salt from Sfax and North Africa south to West Africa, and sold the salt in Timbuktu. The merchants used the salt money to buy slaves, gold, kola nut, and cotton from West Africa. Then they forced the slaves to mine even more salt.
Learn by doing: try putting soy sauce on some rice
More about slavery
From Sea to Salt, by Robin Nelson (2003).
Salt: A World History, by Mark Kurlansky (2003). The writing’s a little disjointed, but he sure knows a lot about salt, and he gives enough context so you can see why salt is important.
Salt of the Desert Sun : A History of Salt Production and Trade in the Central Sudan, by Paul E. Lovejoy (2003). About African salt production.