system
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human
ELI5: Why was salt so historically valuable?

I know that it was hugely important for food preservation etc. but it literally just comes out of the ocean. Especially in hot countries surrounding the Mediterranean, why would you trade so much for salt when you can literally just evaporate seawater yourself?
gpt
>I know that it was hugely important for food preservation etc. but it literally just comes out of the ocean. Especially in hot countries surrounding the Mediterranean, why would you trade so much for salt when you can literally just evaporate seawater yourself?  
  
You are underestimating the gigantic amounts of salt required for food preservation in a per-refrigeration world. The few kilograms you can wrestle out of a primitive Mediterranean desalination setup each day might be enough for a few local fishermen to preserve their catch - not nearly enough for whole continents worth of people.  
You can't equip army supply trains without massive amounts of salt. You can't provision sea voyages. Without having stockpiled salt for **years in advance**, countries couldn't go to war.