In an empirical study on the diffusion of the Isis cult throughout 44 major cities of the Greco-Roman world, Hegedus concludes that the expansion of the Isis cult was linked to an urban location's proximity to Alexandria and Rome. In a similar study, Stark concludes that the diffusion of the Isis cult and Christianity were intertwined. These claims are evaluated in a new study that accesses the impact of city size, distance from Rome, religious pluralism and cultural continuity on the diffusion of the Isis cult throughout 22 major cities of the Roman Empire. Updated data on the diffusion of the Isis cult are utilized and the data are subjected to rank-order correlation analysis and binary logistic regression analysis. Findings indicate that the diffusion of the Isis cult and Christianity was somewhat contemporaneous and that a deregulated Roman religious marketplace provided an opportunity for new religious movements to satisfy an unmet demand for religious products.