Abstract: Religions go hand in hand with different attitudes toward economic issues, such as education, property right protection and attitude towards inventive activity. The Spanish medieval history presents a natural experiment to study how the long lasting presence of different religious denominations, i.e. Christians and Muslims, could have shaped economic outcomes, specifically the production of long-lasting patents. Moreover, the coexistence of such diverse religious doctrines could lead to complementarity or substitutability between religion-related inventive skills, leaving the final answer to an empirical exploration. We address this issue by means of a novel dataset containing detailed data on yearly cell-level (10X10 Km) information on Christian and Muslim presence and data on innovation/patents during the industrial revolution.