On March 28, 1549, the Genoese merchant Jerónimo Cataño submitted a formal request (requerimiento) before a public notary in Seville on behalf of Bartolomé May, a German representative of the Welser company. The accompanying documentation is the foundation for an analysis of the commercial relationships and financial structure of various agents and the mercantile groups they represented. The Provincial Historical Archive of Seville houses an extensive collection of documents that facilitate the reconstruction of these networks, enabling a number of key issues to be explored: what business ventures did they undertake together? What types of commercial instruments did they employ? Which financial centers were interconnected through their activities? How did they leverage their relational capital? This study aims to shed light onto the complex web of commercial and financial relationships between mercantile groups that have traditionally been examined in isolation. The unexpected connections between seemingly disparate groups—so-called weak ties—created new business opportunities that withstood the test of time. Indeed, by 1589, one generation later, their descendants continued to engage in trade together. The wealth of archival material available allows for a systematic mapping of the network, the identification of behavioral patterns, and the analysis of the variables that contributed to the success of certain agents. The application of Social Network Analysis (SNA) metrics and visualization tools provides a robust methodological framework to assess the agency of key individuals who acted as intermediaries within the network. This case study stands as a compelling illustration of Mark Granovetter’s theory on the strength of weak ties.