  Montesquieu describes commerce as an activity that cannot be confined or controlled by any individual government or monarch. This, in his view, has always been true: "Commerce is sometimes destroyed by conquerors, sometimes cramped by monarchs; it traverses the earth, flies from the places where it is oppressed, and stays where it has liberty to breathe" (SL 21.5). However, the independence of commerce was greatly enhanced when, during the medieval period, Jews responded to persecution and the seizure of their property by inventing letters of exchange. "Commerce, by this method, became capable of eluding violence, and of maintaining everywhere its ground; the richest merchant having none but invisible effects, which he could convey imperceptibly wherever he pleased" (SL 21.20). This set in motion developments which made commerce still more independent of monarchs and their whims.