Salt is a biological necessity of human life. But we live our daily lives practically unaware of this basic biological fact. Most of our food already has salt added to it: check the labels on almost any prepared food in the house. But if you are in the habit of baking your own bread, or cooking your own porridge, it's immediately and disastrously obvious if you forget the salt. In ancient times, salt (or the lack of it) could drastically affect the health of entire populations. Trade in salt was very important, and salt was valuable enough to be used as currency in some areas. The Latin phrase "salarium argentum," "salt money," referred to part of the payment made to every Roman soldier, and the word has been carried down the ages into the English word "salary". Everyone must have salt, so it has been a commodity much abused by attempts at monopoly, by individuals, corporations, cities, and nations. The city of Rome may have begun as a salt-trading center, like Venice after it. Certainly the salt traders of the Roman port of Ostia raised the price so high that the state was forced to take over the industry about 506 BC. Man-made salt-ponds along the Mediterranean shore date back to Roman times, and it is inevitable that we will find older ones. Salt was already being mined in the Alps when Rome was founded.
Salt was taxed by governments from the ancient Chinese and Romans to late medieval Burgundy, where salt was taxed at more than 100% as it came from the salt-works. Extended to the whole of France when Burgundy was absorbed, the notorious salt tax "la gabelle" became necessary to the government. Cardinal Richelieu said that it was as vital to France as American silver was to Spain. The repeal of the salt tax was a major goal of the revolutionaries of 1789, but Napoléon restored it as soon as he became Emperor, to pay for his foreign wars: and it continued until 1945. It is said that income from a salt pan in southern Spain largely financed Columbus' voyages....