Archives and libraries are the invaluable but materially vulnerable memory of mankind. While their history is full of destructions, losses, and other interruptions, we still lack studies that problematize the profound consequences of such events. My project changes this by exploring how the first archive and library of Tartu University, the Swedish National Archives, and Greifswald University Library were affected by various disruptions, c. 1650–1815. The main sources are preserved investigations of disruptions, and inventories and catalogues of the respective collections. To deepen the analysis, the cases, and thus archive and library history, are introduced to the innovative field of ignorance studies. In this way, the project offers novel theoretical perspectives on how disruptions have affected the authoritative knowledge institutions of states. By pointing to reorganizations and reinterpretations of collections, my analysis will show how the disruptions made new knowledge. I will also explore the ignorance of archivists, librarians, and other users that the disruptions caused. The project also contributes to scholarship focused on imperial power and infrastructure for knowledge, and adds novelty to this field by exploring cases in the Baltic Sea Region. In conclusion, these historical cases of disruptions can help us deepen our understanding of how knowledge and ignorance interplay in the making of the archives and libraries that our history and scholarship depend on.