Was Caligula Really Insane?

Nobody can diagnose Caligula at a distance of two thousand years, and the sources that call him mad were written by his enemies or long after his death. Caligula (Gaius) ruled from AD 37 to 41, fell seriously ill a few months into his reign, and afterwards ruled with growing cruelty until officers of the Praetorian Guard murdered him in January 41. Suetonius and Cassius Dio describe a madman; many modern historians, notably Aloys Winterling, argue that his outrages were deliberate humiliations of the Roman aristocracy rather than insanity. The famous story that he made his horse a consul is not what the sources say: Suetonius reports only that he was said to have planned it.

The reign

Gaius, nicknamed Caligula (“little boot”) by soldiers when he was a child in his father Germanicus’ camp, became emperor in March AD 37 at 24, to wide popular joy after the last grim years of Tiberius. In the autumn of 37 he fell gravely ill. After his recovery he began to execute or force the suicide of relatives and senators, including his cousin and adopted son Tiberius Gemellus and his father-in-law Silanus. He spent heavily, demanded unusual honours, led a campaign to the northern coast of Gaul that ended without crossing to Britain, and treated the senate with open contempt.

On 24 January AD 41 officers of the Praetorian Guard, led by Cassius Chaerea, killed him in a passage of the palace during games on the Palatine. His wife and infant daughter were killed too.

Why the “mad emperor” is doubted

Only two contemporaries who wrote about him survive in any detail: the philosopher Seneca, who disliked him, and the Jewish writer Philo of Alexandria, who met him on an embassy and found him hostile and erratic. The full narratives, Suetonius (writing about 80 years later) and Cassius Dio (more than 150 years later), draw on a tradition shaped by the senators he humiliated and by the new regime that replaced him.

Read closely, many of the stories describe mockery aimed at the elite: forcing senators to run beside his chariot, the jest about his horse, extravagant shows of divinity. Historians such as Aloys Winterling argue this was a calculated assault on the hypocrisy of the relationship between emperor and senate, cruel but not mad. Others suggest an illness in 37, possibly an encephalitis or a mental breakdown, changed him. Both views agree he was dangerous.

The horse

Incitatus, Caligula’s favourite racehorse, is said by Suetonius to have had a marble stall, an ivory manger and purple blankets, and Suetonius adds that Caligula was said to have intended to make him consul. Cassius Dio repeats the story as a promise. No source says it happened, and many historians read it as a joke at the senate’s expense: a horse could do the job as well as they did.

What most scholars accept, and what stays contested

• Accepted: Caligula reigned AD 37–41; he suffered a severe illness late in 37; he executed relatives and senators; he was murdered on 24 January 41 by Praetorian officers including Cassius Chaerea; Incitatus was never made consul.
• Mainstream: A cruel and autocratic ruler whose reputation for madness rests largely on hostile and later sources.
• Contested: Whether he was mentally ill, and if so what the illness was; how much of the anecdotal tradition is true; how far his behaviour was a deliberate political strategy.

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Sources and further reading

• Aloys Winterling, Caligula: A Biography (University of California Press, 2011)
• Anthony A. Barrett, Caligula: The Abuse of Power (Routledge, 2nd ed. 2015)
• Suetonius, Life of Gaius (Caligula); Cassius Dio, Roman History 59
• Wikipedia, “Caligula” (checked 15 October 2026)