King Louis XIV was upset that so many members of the French nobility were dying off in a hurry. It started in the late 1660s. Autopsies showed the victims' insides were blackened, as it they were rotting. Were they poisoned? Was it witchcraft? At the time, there was only a short leap from alchemy to witchcraft to crime. The king established a special tribunal to investigate a prosecute the murders.
The “Affair of the Poisons,” as it came to be known, is a misleading name for one of the largest witch trials in modern history. Over just five years, from 1677 to 1682, 319 subpoenas were issued, 194 individuals arrested, and 36 executed (with perhaps dozens more dead from suicide, or in prison or exile). In total, it claimed between two and three times as many lives as the Salem witch trials across the Atlantic, 10 years later. It began with what appeared to be an isolated case, but then door after door after door opened, eventually implicating rich and poor alike.
As the events unfolded, suspects were tortured before being killed, and their confessions implicated others, and scandals among the nobility were uncovered. There was definitely some rotten things going on underneath all that wealth and power. You can read an account of the Affair of the Poisons at Atlas Obscura.
(Image credit: Wellcome Library, London)