I analyze the basis of the market economy in classical Rome, from the perspective of personal-versus-impersonal exchange and focusing on the role of the state in providing market-enabling institutions. I start by reviewing the central conflict in all exchanges between those holding and those acquiring property rights, and how solving it requires reducing information asymmetry without endangering the security of property. Relying on a model of the social choice of institutions, I identify the demand and supply factors driving the institutional choices made by the Romans, and examine the economic circumstances that influenced these factors in the classical period of Roman law. Comparing the predictions of the model with the main solutions used by Roman law in the areas of property, businessexchange and the enforcement of personal obligations allows me to propose alternative interpretations for some salient institutions that have been subject to controversy in the literature, and to conclude with an overall positive assessment of the market-enabling role of the Roman state.