Relations between the separatist regime of Marcus Postumus (in about 260 AD) and the Central Empire have been the subject of academic speculation but notably little direct research. It has been postulated that there was no 'closed border' policy between the two empires, and that the apparent exchange of currency substantiates this view. This volume examines the hypothesis, as well as investigating whether the Central Empire coinage was excluded from circulation within the realms of the Gallic Empire, and, similarly, whether the coinage from the Gallic provinces did not circulate widely outside the areas of their control during the lifetime of the regime. The study is intended as a contribution to the development of a reliable method of translating numismatic data into historical language. The appendices include a concordance of the epigraphic sources, hoard tabulations, and a bibliography of hoards and find sites.