The article discusses the scientific history of the retrospective diagnosis of the epidemic outbreak in the retinue of Frederick I Barbarossa in 1167, focussing primarily on the question of what disease it might have been that killed so many people outside Rome. On the one hand, this required interdisciplinary research, whereby it is easy to forget that there are older and younger sciences and that the younger ones were not taken into account. On the other hand, taking the contemporary perspective on experiences is sometimes overlaid by one’s own experiences, so that important details can fall by the wayside and it is then forgotten whose experiences in the contemporary context are the subject of research