Konrad of Megenberg (c. 1309–1374) was a German cleric, natural-philosophy writer, and senior canon of the cathedral chapter of Regensburg from 1342 until his death. His best-known work is the Buch der Natur (‘Book of Nature’, c. 1349) — the first comprehensive natural-history encyclopaedia composed in German rather than Latin, and the substantive German-language source for the European medieval understanding of plants, animals, minerals, weather, and human anatomy. The Buch was reprinted in dozens of editions through the next two centuries and was one of the canonical works of pre-Reformation German vernacular science.

In 1350, while the Black Death was completing its first European passage, Konrad wrote a short separate tract titled De mortalitate in Alamannia (‘On the Mortality in Germany’). The tract substantively defended the German Jewish communities against the conspiracy theory that they had caused the plague by poisoning wells.

What the conspiracy theory claimed

The well-poisoning libel had emerged in late 1348 and substantively driven the substantial Rhineland Jewish pogroms of the following winter and spring — including the 14 February 1349 Strasbourg massacre, the substantial Basel massacre of January 1349, the Cologne massacre of August 1349, and similar events across roughly 200 German and Swiss towns. The conspiracy claim was that Jewish communities had collaborated to poison the Christian-used wells of central Europe with a substance procured from Spain or the Levant. Confessions extracted under torture from a small number of Savoyard Jews in late 1348 had been circulated as the documentary basis for the claim.

Pope Clement VI had condemned the libel in two papal bulls (Quamvis perfidiam, July 1348; Sicut Judaeis, September 1348) and had explicitly ordered Catholic clergy to protect Jewish communities. The substantive papal intervention had limited effect against the popular conspiracy theory.

What Konrad argued

Konrad’s argument was substantively medical-Aristotelian. He worked through the conspiracy claim point by point using the standard Aristotelian framework for epidemic disease (which attributed plague to a corruption of the air rather than to deliberate human poisoning):

  1. The plague was killing Jews at the same rate as Christians, often in the same towns and street networks. If Jews had poisoned the wells, they themselves would not be drinking the poisoned water; they would be substantively immune. They were not immune; they were dying alongside their Christian neighbours. The empirical evidence substantively refuted the well-poisoning hypothesis.

  2. The plague had moved across Europe in geographical patterns consistent with atmospheric and human-contact transmission — south to north, coast to interior, with the characteristic timing of a epidemic disease. Poisoned wells would have produced sporadic isolated outbreaks at specific contaminated water sources. They had not. The plague was geographically wrong for a well-poisoning origin.

  3. The confessions extracted from Savoyard Jews under torture were substantively unreliable as evidence. Konrad noted that torture extracted whatever the torturer wanted to hear; the Savoyard confessions had been substantively driven by the political-judicial needs of the prosecuting authorities rather than by underlying truth. The substantive methodological point was startlingly modern.

He concluded that the well-poisoning conspiracy theory was empirically false, theologically wrong (the Christian moral obligation to protect Jewish communities had been substantively confirmed by the long Sicut Judaeis papal tradition), and politically dangerous (the substantive massacres were destroying communities that had been peaceful neighbours of the German towns for centuries).

What the tract accomplished

The De mortalitate circulated in manuscript through the Bavarian and Bohemian ecclesiastical networks through the early 1350s. Its substantive impact is hard to measure. The Rhineland pogroms had been substantively completed by the time Konrad composed the tract — most of the massacres had taken place in the winter and spring of 1349 — and the Jewish communities affected had been substantively destroyed or expelled before any potential intellectual response could be substantively organised. The substantive long-term cultural impact was the inclusion of the De mortalitate’s arguments in the substantive subsequent German-language anti-libel literary tradition.

Konrad continued at Regensburg through the 1350s and 1360s, writing further natural-philosophy works in German and Latin. He died at Regensburg in April 1374, aged about 65, of natural causes. His cathedral tomb survives.

The substantive German Jewish communities he had defended did not survive the Black Death intact. The substantive surviving Rhineland Jewish population in 1400 was a fraction of its 1340 size, and many of the medieval German-Jewish urban communities never substantively recovered.