The current article was prompted by a chance discovery by one of the authors during archival research in the great Augustinian Abbey of Klosterneuburg directly north of Vienna. Inside carton box K 219, amidst an eclectic collection of miscellaneous documents, there is an envelope with two bullets and a short hand-written note stating that these bullets were shot by Austrian Jägers through the abbey’s windows during the 1809 War. This accidental finding has prompted us to undertake an exciting source-based study which led to a re-discovery of previously unknown military engagement from the War of 1809, and also enables us to explain how it came about that one of the most important monasteries in the Habsburg Monarchy came under friendly fire by Austrian troops.