Salt is important in the alimentation of both humans and animals.
Even if salt must have been consumed by people since prehistory, the first written mentions of the salt used in alimentation come from ancient Egyptians which employed it 5,000 years ago in meat processing.
Later, ancient Greeks used it to make salted fish and the people of the European steppes to prepare extremely salted cheese. 2,200 years ago, Chinese documents during the leadership of the emperor Yu speak about the "salt tribute".
In antiquity, salt was hardly achieved, and Romans used it as currency, hence the world salary from Latin "salarium", derived from the word "sal" (salt), because Roman troops received a salt payment. This way, salt was also used in Africa, Central Asia, Central and North America. Even today in some areas, a cup of salt is exchanged for a sack of cereals.
Salt is extremely abundant in sea water and in the Earth's lithosphere.
In some places large deposits of salt, or even salt mountains of salt are found, remaining after the evaporation of a sea or a salt lake.
Since antiquity, Greeks and Phoenicians extracted salt from seawater by evaporation using sun heat. Seawater was deposed in square basins dug near the shore and left to evaporate, leaving behind pure salt; the method is still used in many places, like Portugal.
In other areas, people obtain salt from salt lakes. In Sahel (Southern Sahara, from Mauretania, Mali to Ethiopia), salt is extracted from salted ground, using the evaporation method. In every exploitation, there are two round decantation basins and many small evaporation basins. Salt exploitation can be made only during the dry season, from November to April.
Men and women carry water (which is also salted) in leather bags from the springs to the decantation basins where it is mixed with the salted ground. The water, whose salt concentration increases sharply, is left to clarify and deposed in the small basins where -under the solar heat - it evaporates. The resulting salt is traded through all Sahara (photo), using the famous "salt caravans".
A similar method is employed in the Bolivian Altiplano, a high dry plateau in the Andes. But many primitive populations did not have easy access to salt before the contact with the Europeans.
In the hinterland of New Guinea salt is extremely rare and many tribes do not know it. Here, the salt springs are also sulfurous, fact that makes the salt toxic.
But the indigenous have found an ingenious solution to get the salt. The spring's water is directed through bamboo pipes in an underground reservoir. Here, the people introduce bundles of extremely dry grass which absorb all the liquid. After that, the bundles are dried in the sun. On the grasses crystals of salt mixed with sulfur are left. In this stage, the grasses are burnt, an operation that removes the sulfur (which oxidizes with air oxygen forming sulfur dioxide) and what is left is ash mixed with salt. The mixture is put in the water and decanted, resulting a saline solution without sulfur. The solution is put to evaporate in the fire, in clay pots covered with banana leaves. The resulting salt is not very pure, but it's all they can get.