The Chinese were the first to view salt production as a major business. From the ninth century BC, they had obtained salt crystals by boiling seawater in clay pots.
This technique would spread throughout the western world, and a millennium later the Roman Empire would still be the most widespread. When the sea was far away, the way was to dig the earth for salt. This is what the Celts did, the inventors of rock salt mining (NaCl). According to archaeological records, they were looking for salt under the ground as early as 1300 BC.
Salt soon became the target of greed by the rulers, who began to tax their trade, commerce and production and to raise large sums of money from it.
In many civilizations, salt extraction was a state monopoly.
Just as it should be available to the average citizen, salt was indispensable to the Roman legionaries, who conquered and maintained the gigantic empire. So much so that soldiers were even paid in salt, from which come the words "salary", "wage" (payment in salt) and "soldier" (the one who received the payment in salt).