I wondered once too often about the origin of this phrase. As I wrote it today, I decided to do something about it. The phrase “worth one’s salt” began with the ancient Romans, perhaps as early as 900 B.C. During that time, soldiers were paid for work in “salarium”, an allowance for the purchase of salt. Salt was a hard-to-find commodity in the ancient world and regarded as good for health. The literal translation of the word “soldier” from that era is “one who is paid in salt”.
Look at the Latin word “salarium” which means “pay”. This was shortened as it appeared in English to salary. When you say that someone is “worth their salt” it means that they are worth the wages that they earn.