Salt: A World History -

: Before modern refrigeration, salt's ability to preserve food was vital for long-distance travel and surviving seasons without fresh food, directly enabling the expansion of early civilizations.

: Salt was once so valuable it was used as currency; the Roman practice of paying soldiers in salt is the origin of the word "salary" and the expression "worth his salt".

: The quest for salt inspired early inventions, such as natural gas furnaces in ancient China and drilling techniques that eventually led to the petroleum age. Salt: A World History: Kurlansky, Mark - Books - Amazon.com