This article considers, first, the roles of Paris, Rome, Venice, and Vienna in the network of Peter Lambeck, the librarian of the Hapsburg emperor Leopold I, and, secondly, Lambeck’s and Vienna’s own places in the Republic of Letters during the period 1662–1680. It begins with a biographical account, in which I situate Lambeck both geographically and intellectually. The importance of Paris is contrasted with his not so positive experience in Rome. Secondly, I focus on Lambeck’s declaration of intent to link Vienna to the Republic of Letters. Thirdly, I survey the eminently Venetian networks through which Lambeck tried to fulfil his intellectual goals. The tensions between France and the Habsburg Empire crashed against Lambeck’s idealistic aims. This raises the issue of the impact of geo-politics on the production and circulation of knowledge in early modern Europe, and prompts questions about openness and secrecy in the Republic of Letters.