In the first part, we study the role of Martin Luther during the early spread of the Reformation, one of the most important religious, political, and economic events of the last millennium. In the second part, we present a new database of the population of books censored by the Catholic Church during the Counter-Reformation period (16th and beginning of 17th centuries) containing information on titles, authors, georeferenced printing places and printers. We identify censored books by topic (religion, sciences, social sciences and arts), language, location of index, and describe patterns of censorship across political entities in Europe over time, using the index produced in Rome, as well as local indexes of prohibited books such as the Index of Louvain and the Index of the Spanish Inquisition. We then test the effects of censorship on the number of printed books, on the location of thinkers, on the spread of Protestantism and ultimately on city growth. Preliminary results suggest that Catholic censorship did reduce printing of forbidden authors, and that defiance of censorship affected city growth and the diffusion of knowledge.