Salt is essential to the functioning of the human organism, and since people started to settle and had no access to daily fresh meat to satisfy their salt needs, salt was required either as a food supplement or for the conservation of meat and vegetables.
In coastal areas, salt was available from the sea, while inland settlements formed in the neighborhood of surface brines on more or less dried salt lakes. People usually followed animal trails to find springs of natural brines, and there are reports that in the main pattern of today’s North American road network and settlements you can still follow the ancient trails of animals and early settlers connecting to sources of naturally occurring salt.
In addition to sea salt, salt lakes, and natural brine sources, rock salt deposits (i.e., in the northern Sahara, ancient Persia, northern Spain, Romania, Lueneburg in Germany) are the fourth source of salt.
Already in pre-historic times, surface brines were not only used as such, but also dried in the sun. In colder and humid climates, the first evidence for evaporation techniques using wood fire and ceramic vessels date back to 5400 BC in Bulgaria.
The first underground drilling for brines and subsequent evaporation in China dates back to at least 800 BC, where bored holes went to a depth of up to 500 meters.
In Europe in the Middle Ages, larger-scale salt production via evaporation of brines started for the needs of a growing population. In the early medieval times in Europe, it was reported that 13 hectares or roughly 34 acres of forest were required to evaporate low-grade brines in Germany which is equivalent to 20 MWh per ton of salt. This led to a massive deforestation. Evaporation techniques progressed rapidly and energy consumption decreased to under <10 MWh/ton by the 18th century. A current value for the same brine type would be in the range of <0.2 MWh/ton of salt. Around 800 BC, underground rock salt mining started in Europe, as well as drilling for underground brine sources.