This research project intends a structural analysis of business networks in Roman long-distance trade. While an integral part of economic history in other pre-industrial societies, the application of network theory in Roman merchant communities remains a striking lacuna. This proposal hence intends to fill this gap by studying the structure of networks Roman businessmen were relying on to organize commerce in a volatile trading world. We will focus on the business communities in Republican Delos on the one hand, and Imperial Puteoli and Ostia on the other. To visualize the networks merchants were cultivating, we first intend a closereading of inscriptions in which individual businessmen and their connections are mentioned. We will distinguish between those based on kinship (family businesses), dependency (networks involving masters, slaves, patrons and freedmen) and what can generally be styled shared experiences (loose connections of coreligionists, members of the same professional association, business partners etc.). In a next stage, the economic relevance and density of these ties will be evaluated. Finally, the results for the Republican and Imperial age will be compared in order to assess whether the unification of the Mediterranean world under Roman rule profoundly altered the business world and the nature of merchant networks. As a working hypothesis, we assume this unification to facilitate commerce, which may be reflected in the creation of larger, wide-spread and more efficient networks.