The monetary system of late medieval and early modern Europe has been commonly described as irrational, in the light of later commodity money standards. In particular, the alterations in the legal value and/or in the metal content of most coins throughout this period have been regarded as a source of disorder and as a product of ignorance and abuse. This article suggests that the whole system, and its apparently awkward articulations, may have been deliberately designed to ensure complementarity between domestic and foreign trade. From this perspective, monetary alterations appear as the levers of a peculiar form of monetary policy, with an extra degree of freedom compared to more modern instruments, and equally open to being managed or mismanaged.