(The censors) also imposed a new tax on the annual salt production. Salt cost a sixth of an as in Rome and throughout Italy; they set it to be offered at the same price in Rome, but more in town squares and marketplaces, and at other rates in other places. It was widely believed that just one of the two censors devised this tax ... As a result (the censor) Marcus Livius was given the nickname 'salt-dealer'.
Livy 29.37.3