The “provincial Saint Bartholomew’s Day Massacres” were not a straightforward copy of the massacres carried out in Paris, beginning on 24 August 1572. Beyond the particular context and dynamics of the events in each city, there were other elements that help to account for the onset of violence, and notably the question of information flows. By examining the particular case of Lyon, the study of the way information about the killing was transmitted and its deployment by the different local actors responsible for its massacre enables us to examine the complexity of the information nexus during the days of the slaughter, and to measure the role played by information in the onset and evolution of the massacres. Rumours, fake news, and official and unofficial messages all flooded into the city, the polyphony of voices creating a confusion that opened the way for the killings. The study of the Saint-Bartholomew’s Day Massacre through the prism of information helps to shed light on the ways in which violence was legitimated and raises the question of news as an agent in the massacres.