In this chapter, the authors follow the first outbreak of the Justinianic plague as closely as their source material allows people, in an effort to make visible the contemporary communication networks both by sea and by land. They look into the possibility of using additional, alternative sources to historiography and chronography for establishing the route of the infection. Diseases, like ideas, travel along with people, their dissemination over a wide geographical frame being a true reflection of the nature and capacities of the actual state of communications of a given society. The Justinianic plague is no exception to this pattern. The study of its dissemination will enable people to look at the internal connections of the Byzantine world at the moment of its greatest territorial expansion. Modern epidemiology, moreover, has developed models that shed light on the mechanism of the plague's dissemination.