Between astrological divination and local knowledge: Prognostics and „epignostics“ related to natural disasters in the Middle Ages

As the term “disaster” (a “corruption of the stars”) shows, the connection between comets, planetary/stellar constellations as well as solar and lunar eclipses on the one hand and (natural) disasters, diseases and other catastrophes on the other hand had been evident for pre-modern societies in Europe. This is particular true for those events that occurred suddenly and could not be explained by local knowledge. However, this relationship had been manifold. Some medieval authors used natural phenomena and disasters to serve as “markers” for a bad reign. Other events such as locust invasions were interpreted as divine punishment and portents of the Last Judgement. Comets such as the one appearing in 1337 were seen as the beginning of a chain reaction leading to locust invasions (1338-1341), extraordinary floods (1342-1343), earthquakes (1348) and Black Death (1347-1352). Therefore, many of the medieval treatises on nature also dealt with comets (Gregory of Tours, Isidore of Seville, Bede the Venerable, Honorius of Autun, Thomas of Cantimpré, and finally Konrad of Megenberg in his Buch der Natur) and their meaning. Finally, astrologers pronounced the coming of a new deluge based on the so-called Toledo Letters, such as for the year of 1524 (which was then actually a very dry year).