The September Massacres were a series of killings of prisoners in Paris that occurred in 1792, from Sunday Sept 2 until Thursday Sept 6, during the French Revolution. Half the prison population of Paris, between 1,176 and 1,614 people, were killed by fédérés, guardsmen, and sansculottes, with the support of gendarmes responsible for guarding the tribunals and prisons, the Cordeliers, the insurrectional commune, and the revolutionary sections of Paris.With widespread fear that foreign and royalist armies would attack Paris, and that the imprisoned Swiss mercenaries would be freed to join them, on 1 September the Legislative Assembly called for volunteers to gather the next day on the Champs de Mars. On 2 September, around 1:00 pm, Georges Danton, delivered a speech in the assembly, stating: "We ask that anyone refusing to give personal service or to furnish arms shall be punished with death. The bell we are about to ring... sounds the charge on the enemies of our country." The massacres began around 2:30 pm in the middle of Saint-Germain-des-Prés, and within the first 20 hours more than 1,000 prisoners were killed.

The next morning, the surveillance committees of the commune published a circular that called on provincial patriots to defend Paris by eliminating counter-revolutionaries, and the secretary, Jean-Lambert Tallien, called on other cities to follow suit. The massacres were repeated in a few other French cities, in total 65–75 incidents were reported.The exact number of victims is not known, as over 440 people had uncertain fates, including 200 Swiss soldiers, (or 22?). The identity of the perpetrators, called "septembriseurs", is poorly documented, but a large number were Parisian national guards and provincial federates who had remained in the city since their arrival in July. 72% of those killed were non-political prisoners including forgers of assignats (galley convicts), common criminals, women, and children. 17% were Catholic priests.The minister of the interior, Roland, accused the commune of the atrocities. Charlotte Corday held Jean-Paul Marat responsible, while Madame Roland blamed Georges Danton. Danton was also accused by later French historians Adolphe Thiers, Alphonse de Lamartine, Jules Michelet, Louis Blanc and Edgar Quinet of doing nothing to stop them.According to modern historian Georges Lefebvre, the "collective mentality is a sufficient explanation for the killing". Historian Timothy Tackett deflected specific blame from individuals, stating: "The obsession with a prison conspiracy, the desire for revenge, the fear of the advancing Prussians, the ambiguity over who was in control of a state that had always relied in the past on a centralized monarchy: all had come together in a volatile mixture of anger, fear, and uncertainty."