From autumn 1793 to summer 1794 the revolutionary government ruled through fear, in the name of saving the Republic. The period is called the Terror because its leaders used that word themselves.
The machinery
On 5 September 1793 sans-culottes invaded the Convention demanding action against hoarders and traitors, and the deputies declared terror "the order of the day." The Law of Suspects (17 September 1793) allowed arrest on vague grounds of hostile views or connections: anyone who "by their conduct, their relations, their remarks or their writings" showed themselves partisans of tyranny or enemies of liberty. Days later the General Maximum capped the prices of grain and other necessities, and wages too.
Power gathered in the twelve-member Committee of Public Safety. It included Robespierre, who joined in July 1793, his young ally Saint-Just, and Lazare Carnot, the engineer who organized the new mass armies. Representatives on mission carried the Committee's authority into the provinces. The guillotine, adopted in 1792 as a humane and equal way to kill, since nobles and commoners would now die the same way, became the symbol of the age.
Who died, and where
Marie Antoinette was executed on 16 October 1793, the leading Girondins at the end of the month. About 17,000 people were officially sentenced to death across France. Many more died in prison or were killed without trial; estimates of the total run to about 35,000 to 40,000, though such figures are uncertain. Most executions took place in regions in revolt, such as the west and the Rhône valley, rather than in Paris. Contrary to the popular picture, most victims were commoners of the Third Estate; nobles and clergy together were well under a fifth.
The worst killing came in the civil war. After the Vendée rebel army was crushed in December 1793, "infernal columns" burned villages and killed civilians, and at Nantes the representative Jean Baptiste Carrier had thousands of prisoners drowned in the Loire. Deaths from the Vendée war on both sides may have reached 150,000 or more; the numbers are disputed, and so is whether the word genocide fits, which most historians reject while accepting that atrocities were committed.
Virtue and terror
Robespierre gave the Terror its theory in February 1794. He held that popular government in revolution must rest on virtue and terror together: "If the mainspring of popular government in peacetime is virtue, the mainspring of popular government in revolution is at once virtue and terror: virtue, without which terror is fatal; terror, without which virtue is powerless."
The revolutionaries also tried to remake daily life. A revolutionary calendar counted years from the founding of the Republic and divided months into ten-day weeks, with months named for weather and harvests. A campaign of dechristianization closed churches and turned Notre-Dame into a Temple of Reason. Robespierre, who thought atheism aristocratic, staged a Festival of the Supreme Being in June 1794.
The Terror also devoured revolutionaries. The ultra-radical followers of Jacques Hébert were executed in March 1794. In April Georges Danton and his allies, the "Indulgents," went to the guillotine, because Danton had called for clemency and an end to the Terror. The Law of 22 Prairial (10 June 1794) removed defense counsel and left juries only two verdicts, acquittal or death. In the next seven weeks the Paris tribunal sent more people to their deaths than it had in all the months since it was created.
Why did it happen?
Historians offer two broad answers. The "circumstances" explanation stresses war, invasion and civil war: foreign armies on the frontier, rebellion in the west and south, generals defecting and real conspiracies made emergency rule seem necessary, and the Terror ended when the danger eased. The "ideology" explanation, associated with François Furet, points to the revolution's own logic: a government that claimed to embody a single national will could treat disagreement as treason, which is why the killing in Paris rose even as the armies began winning. Many historians now combine the two, adding fear, factional rivalry and local revenge.
Worked example: reading the Law of Suspects
Set two texts side by side. Article 9 of the 1789 Declaration says every person is presumed innocent until declared guilty. The Law of Suspects, passed four years later by men who revered that Declaration, let committees arrest people for their "relations" and "remarks." Ask how a suspect could prove they were not hostile to liberty. There was no clear answer, because the law punished attitudes rather than acts. The burden of proof had silently flipped.
The lesson is not that the revolutionaries were hypocrites. Most believed the Republic, and with it the rights of man, would die unless they acted. The lesson is that rights are most at risk exactly when leaders sincerely believe an emergency requires suspending them, which is why later rights charters tried to list the protections that no emergency may override.