Assassination of Caligula (AD 41): The Murder of an Emperor

The assassination of Caligula on 24 January AD 41 is generally regarded as the first certain murder of a reigning Roman emperor. Gaius Caesar, known as Caligula, was stabbed to death by officers of his own Praetorian Guard in a passage of the palace on the Palatine Hill in Rome. His killing ended a short, notorious reign and showed that the guard, not the Senate, now decided who ruled the empire.

A popular heir

Gaius Julius Caesar Germanicus was born at Antium (modern Anzio) on 31 August AD 12. He was the son of Germanicus, a celebrated general and adopted grandson of Augustus, and of Agrippina the Elder, Augustus’s granddaughter. As a small boy in his father’s camps on the Rhine he wore a child-sized soldier’s boot, the caliga, and the soldiers called him Caligula, “Little Boot”. He reportedly disliked the name, and it was never part of his official title.

His family suffered badly under the emperor Tiberius. His mother and two elder brothers died in exile or prison after falling foul of the regime. Gaius survived by keeping quiet and living from AD 31 at Tiberius’s court on Capri.

When Tiberius died at Misenum on 16 March AD 37, the Praetorian prefect Macro helped Gaius take power. The Senate granted him the powers of an emperor within days, setting aside Tiberius’s will, which had made his young grandson Tiberius Gemellus a joint heir. As the son of the popular Germanicus, the new emperor was welcomed with enthusiasm.

From hope to fear

The first months were generous. Caligula recalled exiles, paid out Tiberius’s bequests to the people and the soldiers, and staged lavish games. In October AD 37 he fell seriously ill. Ancient writers saw his recovery as a turning point, after which his behaviour grew erratic and cruel, though modern historians are cautious about this neat story.

Within a year Gemellus and Macro had been forced to die. In June AD 38 Caligula’s beloved sister Drusilla died, and he had her declared a goddess. In AD 39 he uncovered a conspiracy involving Gnaeus Lentulus Gaetulicus, commander on the Upper Rhine, and his own brother-in-law Marcus Aemilius Lepidus; both were executed and his surviving sisters exiled.

In AD 39 he built a bridge of boats across the bay between Baiae and Puteoli and rode over it in triumph. He then led an army to the Rhine and to the coast facing Britain, but the planned invasion did not happen. Suetonius claims he ordered his soldiers to gather seashells as “spoils of the ocean”; the episode remains unexplained and may be distorted. Relations with the Senate collapsed amid treason trials, confiscations and public humiliations of senators.

He also provoked a crisis in Judea. In AD 40 he ordered a statue of himself to be set up in the Temple in Jerusalem, an act that would have caused revolt. The governor of Syria, Publius Petronius, delayed carrying out the order, and the king Herod Agrippa I, a friend of the emperor, persuaded him to drop it. The Jewish philosopher Philo of Alexandria, who led an embassy to Caligula at this time, left an eyewitness account of a mocking and unpredictable ruler.

The plot

By late AD 40 many people had reason to want Caligula dead. The leading figure was Cassius Chaerea, a tribune of the Praetorian Guard. According to Suetonius and Josephus, the emperor repeatedly mocked him by giving him obscene or effeminate watchwords. Chaerea was joined by another tribune, Cornelius Sabinus, and, the ancient sources suggest, by one or both Praetorian prefects, by senators and by courtiers such as the freedman Callistus.

The conspirators chose the Palatine Games, a festival held each January in honour of Augustus, when the emperor would be in a crowded temporary theatre on the Palatine. Several earlier opportunities had passed. The ancient writers also report that Caligula was planning to leave Rome for Alexandria, which would have put him out of reach and gave the plot added urgency.

The killing

On 24 January AD 41, around midday, Caligula left the theatre to bathe and eat. He took a covered passage, a cryptoporticus, through the palace, stopping to speak to a group of noble youths from Asia Minor who were to perform. There Chaerea struck him, and Sabinus and others joined in. Suetonius says he received thirty wounds.

His German bodyguard, recruited from tribesmen loyal to the imperial family rather than to Rome, arrived too late to save him and killed several people in revenge, some of them uninvolved senators. A centurion then killed his wife, Milonia Caesonia, and their infant daughter, Julia Drusilla. His body was half-burned in haste and buried in the Gardens of Lamia, according to Suetonius. Caligula was 28 years old and had ruled for just under four years.

Josephus gives the most detailed account, in Book 19 of his Jewish Antiquities, probably based on a source close to events. Suetonius and Cassius Dio broadly agree with it, though details such as the order of blows differ.

Claudius and the Senate

The assassins had no clear plan for what came next. The consuls summoned the Senate to the Capitol, and some senators spoke of restoring the Republic and ending rule by emperors altogether. Others hoped to become emperor themselves.

Meanwhile soldiers plundering the palace found Caligula’s 50-year-old uncle, Claudius, hiding behind a curtain. They took him to the Praetorian camp, where he was acclaimed emperor and promised the guards a large cash gift. With the soldiers behind him and the Senate divided, the senators gave way the next day. Claudius had Chaerea executed, together with some of the plotters, while pardoning most others.

Myths and facts

Caligula’s reputation comes almost entirely from hostile writers: Seneca and Philo, who knew him, and Suetonius and Cassius Dio, writing generations later. Tacitus’s account of his reign has been lost.

• “He made his horse a consul.” Suetonius says only that Caligula reportedly planned to make his horse Incitatus a consul. It never happened, and it may have been a joke at the Senate’s expense.
• “He was clinically insane.” Ancient authors called him mad, and modern writers have suggested illness. Many historians, such as Anthony Barrett and Aloys Winterling, argue that his acts were often calculated, if brutal, moves in a power struggle with the aristocracy.
• Incest and other scandals. Stories of incest with his sisters appear in Suetonius as rumours and are doubted by many modern scholars.

Timeline

• 31 August AD 12: Gaius is born at Antium.
• 16 March AD 37: Tiberius dies; within days the Senate grants Gaius imperial powers.
• October AD 37: Caligula suffers a serious illness.
• June AD 38: His sister Drusilla dies and is deified.
• AD 39: Conspiracy of Gaetulicus and Lepidus; the emperor leaves for the Rhine.
• AD 40: Planned invasion of Britain abandoned; crisis over the statue in the Jerusalem Temple.
• 24 January AD 41: Caligula is killed on the Palatine, with his wife and daughter.
• 25 January AD 41: Claudius is recognised as emperor by the Senate.

Why it matters

Caligula’s murder exposed the basic weakness of the system created by Augustus: the Senate could kill an emperor, as it had killed Julius Caesar, but it could not restore the Republic. Power now rested with the army and the Praetorian Guard, a lesson repeated when Nero fell in AD 68 and through the following centuries.