At the height of the Republic's era of provincial expansion (roughly the first and second centuries BC until the end of the Republic) the Roman tax farming system was very profitable for the publicani. The right to collect taxes for a particular region would be auctioned every few years for a value that (in theory) approximated the tax available for collection in that region. The payment to Rome was treated as a loan and the publicani would receive interest on their payment at the end of the collection period. In addition, any excess (over their bid) tax collected would be pure profit for the publicani. The principal risk to the publicani was that the tax collected would be less than the sum bid.
By New Testament times, publicans were seen chiefly as tax collectors by provincial peoples. It is in this sense that the term is used in Jesus' parable of the Pharisee and the Publican. However, their role as public contractors, especially as regards building projects, was still significant.
With the rise of a much larger Imperial bureaucracy, this task of the publicans, as well as their overall importance, declined precipitously. Evidence for the existence of publicans extends as far back as the 3rd century BC, although it is generally assumed that they existed at still earlier times in Roman history. Knowledge of a tentative terminus post quem is taken from the histories of the 1st century AD Imperial historian Livy.
By the time of the Renaissance, the word "publican" meant a tavernkeeper (the licensed landlord of a public house), and by extension a slang term for a pimp.
In England in the late 12th century there existed a religious sect called the publicani. Among their beliefs was the view that procreation was a sin. This sect was thought heretical and was commonly persecuted in the 1180-1190s by Archbishop William of Rheims (reigned 1176-1202). This is mentioned in Banks and Binns' introduction to the Otia Imperialia, a 13th century work by Gervase of Tilbury.