The defence of Late Byzantine (fourteenth–fifteenth centuries) frontier zones frequently became the responsibility of military elites, borderlords, who enjoyed absolute power in these areas and immunity from any fiscal or other obligation towards the Byzantine state. In this article I present the case studies of two borderlord families: the brothers and military officials Alexios and John, and the Genoese family of the Gattilusi, who ruled large areas around the Northern Aegean in the fourteenth and fifteenth centuries and participated actively in their defence at a time when they were surrounded by enemies and plagued by piracy. The aim of the article is twofold. First, I consider the borderlords’ building activities, modes of self-representation and the creation of new geographies as strategies for establishing control and legitimising their power. Second, I explore how the rise of these borderlords fits with Byzantine imperial policies and corresponds to changes in the character of Late Byzantine imperial authority and the role of the Byzantine emperor within and beyond the empire. Over the course of this article I hope to highlight the complexity of the political and economic situation in the fourteenth and fifteenth centuries and contribute to an understanding of modes of Late Byzantine government and power that move beyond simplistic frameworks of decline and fall.