The ancients knew that of all the things required for the support of human life salt was the most essential.
The Romans called this element sal, and whenever the Roman soldier was sent to a foreign land he was given, over and above his regular pay, an amount of money for the purchase of salt.
This was called his salarium, salt money. The amount varied, because salt might be hard to get and expensive in one country, but cheap and plentiful in another.
Later, after the days of Augustus, salarium denoted the sum of money which a military officer or a governor of a province or a like official received at intervals, in addition to various supplies in kind.
And still later, by the end of the third century A.D., all connection with the original notion of salt money had passed away and salarium, or salary, carried no more than the present meaning, “monetary payment at stated intervals.”