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Why did Cicero order the execution of Catiline’s Roman conspirators?

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Marble bust of Marcus Tullius Cicero, shown with short hair and draped clothing, displayed against a black background. — Cicero Marcus Tullius Cicero, detail of a marble bust; in the Capitoline Museums, Rome.

Cicero ordered the execution of the conspirators because they were planning an armed insurrection and arson within Rome to overthrow the government.12

While Cicero had long suspected Catiline of seditious intentions, he initially struggled to convince the Senate of the immediate danger. The situation changed on December 3, 63 BCE, when Cicero secured signed documents from envoys of the Allobroges, a Gallic tribe, which provided undeniable proof of the conspiracy.12

Following this discovery, the conspirators remaining in Rome were arrested. Although there was debate in the Senate—with Cato the Younger advocating for execution and Julius Caesar arguing against it—the Senate became thoroughly alarmed by the evidence and authorized the executions, which were carried out on December 5 under Cicero’s responsibility. This decisive action was intended to preserve the state and was later celebrated by many as the climax of his career.12