This chapter analyses how the circulation of credit certificates linked to forced loans from the Spanish Crown, secured against the American treasury in the sixteenth century, contributed to the development of an early financial market operating parallel to the banking system. We reconstruct both quantitatively and qualitatively the financial networks that emerged in Seville during the reign of Charles V and the early years of Philip II’s reign among forced lenders, who suffered requisitions of remittances executed by officials of the Casa de la Contratación. Employing Social Network Analysis tools, we identify the most significant actors and examine the extent to which the network structure resembles the operation of a proto-financial market.