 The Minim friar Marin Mersenne (1588–1648) played a central role in French intellectual life of the first half of the seventeenth century. At a time when scientific periodicals were still sorely lacking, he was rightly referred to as “The Secretary of Learned Europe” (“le secrétaire de l’Europe savante”, Hauréau 1877, p. 177) thanks to his sprawling correspondence, which extended his network across the whole of learned Europe, to his role as translator, editor, disseminator of scientific information, and to his ability to generate research and discoveries by creating “fine questions” (de belles questions, Pascal 1658, p. 1) addressed to the foremost scholars of the time. His tireless activity certainly helped to create a new image of a mathematical, mechanistic and experimental science in the making, based on the exchange of information and co-operation between European scholars. Part of his fame is also due to his lifelong connection to Descartes. From the time the latter settled in Holland, Mersenne was his main, and at times unique, correspondent, providing him with rich information on intellectual life, and relentlessly questioning him on philosophical and scientific matters.