Soap was once used as currency in medieval Europe. People valued the 1 lb bars so highly that over time the original purpose of soap as a cleaner was ignored and forgotten. By the late 1300s Europe was an exceptionally foul smelling and filthy place. Arab traders called it "Immund Em Etic" (Unclean Land Causing Vomit) and for generations would only do business through middlemen.

Source : High, Gene. Europe in the Dark Ages, 1910.