On 24 January AD 41, Praetorian officers attacked the Roman emperor Gaius Caesar, commonly called Caligula, in a covered passage on the Palatine Hill. The guard was supposed to protect the emperor in Rome. Instead, two of its tribunes, Cassius Chaerea and Cornelius Sabinus, led the men who struck him as he left performances for the Palatine Games. His own guards killed him inside the imperial residence.
Caligula was twenty-eight when he died, after ruling for less than four years. Relations with senators and members of his court had deteriorated badly, and some of those involved in the murder feared for their own safety. Others seem to have hoped the emperor’s death would allow Rome to dispense with emperors altogether. Yet the conspirators had made no agreement about who should replace him, leaving the succession unresolved.
The Senate began discussing the possibility of recovering the political freedom Rome had possessed before imperial rule. Meanwhile, other Praetorians located Caligula’s uncle Claudius in the palace and escorted him to their barracks. Within hours, the same guard that had furnished his assassins was now backing his successor. Our ancient sources agree on this political outcome while differing over the sequence of the attack, the identities of everyone involved and the aims of the plot.
Why Caligula had become vulnerable
Gaius succeeded Tiberius in March AD 37. He was Germanicus’s son and, through Agrippina the Elder, a great-grandson of Augustus. His place in the family that had established the principate, Rome’s government under an emperor, strengthened his position even though consuls, senators and other traditional magistrates continued to hold office. The new ruler initially enjoyed a warm reception. He made payments and public gestures calculated to reassure the army and the people of Rome.
The early enthusiasm gave way to a serious conflict with the Senate. By AD 39, Caligula had denounced influential figures as conspirators, removed or executed powerful men and exiled his sisters Agrippina and Julia Livilla following the affair involving Marcus Aemilius Lepidus. Ancient historians depict a court where denunciations, humiliations and the emperor’s suspicions made high office perilous. Individual anecdotes are not always independently verifiable, but Cassius Dio’s account of the events of AD 39 and 40 describes repeated purges and confrontations that help explain why prominent Romans feared the emperor.
The surviving narratives reflect the concerns of their authors. Suetonius composed his biography of Caligula decades later, and Cassius Dio wrote later still; both selected stories of cruelty, sexual behavior and supposed madness to illustrate a ruler’s moral failure. The relevant continuous portion of Tacitus’s history has been lost. These texts cannot be treated as a list of medically or historically proven incidents, much less as a basis for diagnosing Caligula. Anthony Barrett and John Yardley stress in their 2023 study of the assassination that the political setting remains obscure and that several influential participants cannot be assigned secure roles.
The principate placed formidable powers in one man’s hands without supplying an uncontested mechanism for removing him. The emperor could direct troops and appoint officials, but his position still required the cooperation of the imperial family, the Senate, military officers and court administrators. As Caligula distrusted more of these people, some came to believe continued loyalty exposed them to danger. The danger came from men already admitted to his daily surroundings, where an armed officer had much better access than any distant opponent.
Cassius Chaerea and the Praetorian officers
Cassius Chaerea served as a Praetorian tribune, an officer with command responsibilities rather than a mere palace servant. The guard consisted of military units stationed at Rome and around the capital, where they could secure the ruler and carry out his orders. Its senior officers therefore possessed unusually close knowledge of imperial movements. They knew the emperor’s movements, including moments when his larger entourage was absent.
Chaerea had already demonstrated military courage. Tacitus, Annals 1.32 describes his actions during the Rhine mutinies of AD 14, when he forced his way with a sword through hostile soldiers. Tacitus calls him a brave young serviceman. Some retellings incorrectly turn this episode into an escape from the annihilation of Varus’s legions in the Teutoburg Forest in AD 9. The surviving passage describes a different incident five years later and offers no evidence that Chaerea fought in that earlier disaster.
Suetonius and Dio both connect Chaerea’s hostility to humiliations inflicted by Caligula. In Suetonius, Caligula 56, the emperor mocks the officer’s masculinity, issuing obscene or sexually suggestive watchwords invoking Venus and Priapus and accompanying them with insulting gestures. The watchword was an ordinary military password passed between personnel on duty, which made its misuse especially humiliating for a commander. The precise exchanges cannot be verified. Still, both authors describe personal resentment as a motive for the plot.
Josephus gives Chaerea a more public motive: he presents the tribune as a man resolved to free Rome from a tyrant. The account admires the killer and may reproduce the political language used by the conspirators to defend their conduct. Anger at repeated insults and opposition to Caligula’s rule could readily have existed together. A guard officer was in a position to help overthrow the ruler he was employed to protect.
Cornelius Sabinus, another Praetorian tribune, was the second principal attacker. In Josephus’s account, Sabinus was already receptive when Chaerea discussed killing Caligula with him. Their combined authority helped them approach centurions, make arrangements within the palace and select a point in the emperor’s routine when his escort might be thin. The ancient narratives describe discussions and missed opportunities before the attack. It was planned by men familiar with the security they intended to defeat.
How large was the conspiracy?
The number of people who knew of the plot remains uncertain. Josephus, Antiquities 19.1 recounts meetings among Chaerea, Sabinus and figures such as Annius Vinicianus and Minucianus. He also describes approaches to Marcus Arrecinus Clemens, a Praetorian prefect. Prefects stood above tribunes in the command structure, making their response potentially decisive. But Josephus’s account repeatedly shows uncertainty and hesitation. Being approached by conspirators or learning their intentions does not establish that a person helped carry out the murder.
Suetonius and Dio also implicate influential freedmen at court as well as serving officers. An imperial freedman had once been enslaved but could, after manumission, wield considerable authority by handling correspondence, administration and access to the emperor. Callistus, one of these powerful courtiers, figures in descriptions of the tensions preceding Caligula’s death. Whether he actively helped the plot or worked for a particular successor remains uncertain. The surviving evidence cannot place every named courtier within one coordinated conspiracy.
The evidence does not support a Senate-wide committee secretly working to restore the Republic. Some senators may have wanted Caligula removed, others may have dreaded exposure, and many could have waited for an outcome before declaring themselves. Josephus reports shifting conversations among separate circles of powerful people rather than a documented roster of conspirators. Dio suggests that knowledge of the plot spread widely through the palace, but his sweeping claim is difficult to substantiate. After a successful assassination, association with the victors could also have looked politically useful.
Nor does the evidence establish that Chaerea’s associates agreed on a successor. Opposition to Caligula could unite a would-be republican, someone willing to accept another princeps and a courtier desperate to stay alive. Their differences mattered as soon as the emperor was dead. The men who planned the murder had no common plan for governing afterward.
The Palatine Games and the covered passage
The occasion was the Palatine Games, with performances linked to the imperial household. Suetonius dates the murder to the ninth day before the Kalends of February. Because Roman dates were counted inclusively, this was 24 January. After attending the entertainment, Caligula was setting out for his midday meal. Moving from a public performance into the palace corridors created an opening for the plotters when his location and direction of travel were known.
Ancient authors place the attack in a relatively narrow or covered passage on the Palatine Hill, above the Roman Forum and amid the imperial residences. Suetonius says Caligula paused to watch young performers from Asia rehearsing there. Dio instead mentions youths summoned from Greece and Ionia. Josephus offers a detailed account of arrangements that day and of the conspirators’ growing anxiety that their chance would slip away. Despite their differences, each places the attack while the ruler moved through a confined route away from the main assembly.
No surviving corridor can be identified conclusively as the murder site. The Palatine contains many vaulted passages, and excavations have encouraged proposals about the location. In 2008, reports linked a newly exposed cryptoporticus to the assassination. A cryptoporticus is a roofed passage, often partly underground, which fits the general sort of space described by the ancient authors. None of the descriptions identifies a feature that would establish which passage Caligula entered.
Chaerea and Sabinus needed to strike before loyal soldiers could intervene. Their ranks allowed them to remain close to Caligula without immediately attracting suspicion. Crowds at the festival, the shifting positions of attendants and the move toward lunch helped create an opening. Josephus recounts earlier delays, and Dio likewise says the conspirators had previously held back. Once the emperor was moving, the officers needed to act before the larger palace guard could respond.
Who struck Caligula first?
There is no single ancient account of who landed the opening blow. Suetonius, Caligula 58 preserves two alternatives. One has Chaerea strike from behind at the neck while Sabinus attacks the front of Caligula’s body. In the other, Sabinus asks for the military watchword, receives the answer Jupiter and strikes the emperor’s jaw. The disagreement is in Suetonius’s own text. The two versions cannot be combined into a single sequence without going beyond the evidence.
Josephus offers further detail but gives a different arrangement of the violence. In his account, Chaerea’s blade strikes between the shoulder and neck and meets the collarbone; Caligula attempts to flee before Sabinus throws him down and other men join in. Josephus names Aquila as the man who delivered the final lethal stroke, although he treats Chaerea as the plot’s driving force. Dio concentrates instead on the attackers’ ferocity and even alleges that some tasted the emperor’s flesh. The episode reflects Dio’s taste for sensational detail. There is no independent physical evidence for it.
Suetonius says the body received thirty wounds and that blows were directed at the emperor’s genitals. These are details in a literary account written after the event. No surviving remains or medical documentation allow the count or the position of each wound to be checked. The attack killed Caligula, but modern descriptions of individual wounds and mutilation cannot be treated as forensic findings.
Caligula was twenty-eight at his death, having governed since March AD 37. His reign therefore lasted less than four years, although ancient writers differ slightly in their reckoning of its duration. The ancient accounts disagree over the wounds and the attack’s precise sequence, but agree on the central event: Praetorian officers killed the emperor whom their military institution existed to defend, inside his palace complex during a festival.
The loyal guards and the murder of Caesonia and Drusilla
Other armed men moved against the assassins. Suetonius says Germanic guards assigned to Caligula raced toward the scene and killed both some attackers and people who had no part in the plot. Josephus similarly describes Germanic soldiers hunting the killers and striking down men they encountered. The Praetorian Guard itself had not collectively decided to murder Caligula; some members were appalled by what had happened. The retaliatory violence helps explain the assassins’ dependence on surprise and the speed with which their control evaporated after the alarm.
Two more deaths followed: Caligula’s wife, Milonia Caesonia, and their little daughter, Julia Drusilla, were murdered. Several ancient accounts attest their fate while differing over where the killings happened and who carried them out. Suetonius describes a centurion stabbing Caesonia and the child being killed by a blow against a wall. Josephus instead says Chaerea dispatched Julius Lupus to murder them. He calls Lupus a tribune, whereas Suetonius identifies Caesonia’s killer as a centurion; a 2021 study devoted to Julius Lupus examines that disagreement. Their disagreement leaves the killer’s identity and rank uncertain. The murders may have aimed to prevent members of Caligula’s household from becoming the focus of loyalist resistance or competing claims to power.
There is no evidence that the deaths of Caesonia and Drusilla formed part of an agreed plan to eliminate the Julio-Claudian family. Claudius, Caligula’s uncle, remained alive, as did other relatives. The assassins had not even settled what government they intended to establish. Josephus describes unease among some conspirators about the women’s and child’s deaths, and opposition to Caligula cannot be equated with support for those killings. The immediate household was targeted amid the uncertainty after the murder, without evidence of a universally endorsed policy to eliminate the dynasty.
The Senate tried to decide Rome's future
With the emperor dead and no undisputed heir, Rome’s traditional institutions briefly had a chance to assert themselves. The Senate still embodied the old Republic’s political authority, and the consuls remained the highest-ranking regular magistrates. Senators could now argue over whether a replacement emperor should be chosen and, more radically, whether imperial rule should continue at all. The Senate still needed a way to enforce any decision against armed opposition.
Dio reports that the consuls assembled the Senate on the Capitoline Hill and secured the public treasury with troops, a practical precaution when control of money and soldiers might decide the succession. Suetonius says some senators urged a return to republican government and even discussed stripping honors from the Caesars. Debate alone could not restore the old constitution. The Republic had been gone for generations, while troops loyal to different leaders occupied Rome. A senatorial resolution alone could not compel those armed men to surrender their influence.
The crisis exposed the differences between the Roman Republic and the imperial system. Augustus had kept traditional offices while combining extraordinary military, political and financial powers in his own position. Those republican forms still survived under Caligula, yet the Senate did not directly command the emperor’s soldiers or resources. After his murder, senators could debate Rome’s future only so long as the armed forces allowed them to turn debate into action.
Josephus describes supporters of the Senate and Praetorian factions disputing who should govern while soldiers considered which arrangement would protect their interests. Among the senators themselves, some favored a new emperor, some demanded republican liberty, and they could not unite around a single candidate. This indecision benefited the guards who were already rallying to Claudius. Rome did not experience a restored Republic lasting two days. It was an unstable interregnum during which rival groups sought to claim authority before any settlement was accepted.
Claudius emerged from the palace
Claudius, Caligula’s uncle and Germanicus’s brother, was another member of Augustus’s extended dynasty. Although he had previously been consul, he had spent much of his life outside the center of public command. Ancient authors dwell on his disabilities and awkward public manner. Such descriptions provide no reliable measure of his political judgment. When Praetorians looked for a ruler with a recognizable dynastic claim, his connection to the imperial family gave him an advantage over senators who lacked one.
The famous story of Claudius hiding behind a curtain comes from Suetonius, Claudius 10. According to that account, he fled into a palace apartment, concealed himself behind drapery beside a balcony, and was discovered when a soldier noticed his feet. Recognized and saluted as emperor, Claudius was carried in a litter to the Praetorian camp, where he spent the night while senators argued elsewhere. Dio also says soldiers found him hiding in the palace and removed him to their headquarters, although he does not repeat every dramatic feature. The curtain is a feature of Suetonius’s story, not an independently verified detail.
Some modern scholarship questions whether Claudius was as helpless as that story suggests. Roberto Cristofoli’s 2016 study considers the possibility that he knew something of the conspiracy and acted more deliberately to secure the succession. This remains a hypothesis drawn from incomplete and difficult sources. The accounts support a narrower conclusion: a section of the Praetorians chose to support Claudius, and the Senate ultimately accepted him as emperor.
Chaerea’s associates had not chosen Claudius as their successor in advance. Josephus even portrays Chaerea as opposing renewed imperial rule and disliking Claudius as a candidate. For the Praetorians who backed the uncle, retaining an emperor protected the pay, standing and influence that the guard enjoyed under the principate. Claudius also offered continuity with Augustus’s family. Claudius secured power with military backing after the assassination. That does not mean all Praetorians had plotted the murder or supported his succession from the beginning.
Claudius made the soldiers a substantial promise. Suetonius records a donative, a cash payment offered to troops, of 15,000 sesterces to each Praetorian after their oath of allegiance. It was a large reward, though comparisons with regular military pay depend on the type of soldier and the period being measured. Suetonius condemns the transaction and calls Claudius the first Caesar to buy military fidelity this way. Earlier emperors had also given money to soldiers, so that formulation reflects his judgment rather than an uncontested first. The payment strengthened Claudius’s hold on the soldiers who had installed him.
Claudius also commemorated the guard’s support on coinage. A silver denarius of Claudius dated AD 41 to 42 in the British Museum carries a representation of the Praetorian camp on its reverse. The museum connects the design with Claudius’s escort to the camp and proclamation by the soldiers. It depicts neither Caligula nor the fatal passage. Produced soon afterward by the successor’s government, it shows the official emphasis placed on the guard’s role in installing him, recording the new regime’s priorities rather than the hostility of later literary accounts toward Caligula.
What happened to the assassins?
Claudius now faced a problem of his own. He owed his position in part to the emperor’s violent removal, but he could hardly declare that palace guards had the right to kill any ruler they disliked. His own security required military officers to respect their oaths. The new emperor also faced men who, during the succession struggle, had publicly argued against emperors or against Claudius himself.
Chaerea paid for the assassination with his life. Josephus reports that Claudius consulted advisers who could approve of Caligula’s removal yet condemn the treachery of those sworn to guard him. Chaerea was executed, as was Julius Lupus, whom Josephus blames for killing Caesonia and Drusilla, together with other participants. Suetonius, Claudius 11 also records the executions of certain tribunes and centurions, partly because they had demanded Claudius’s death. He punished men whose actions had made his reign possible.
Josephus assigns Sabinus a different fate. Claudius allegedly pardoned the tribune and even offered to let him continue in his position, but Sabinus killed himself rather than forsake the republican cause he believed he had served. Josephus admires that commitment, and his account should be read with that sympathy in mind. Josephus’s story exposes the contradiction: men who presented the murder as an act of liberation had helped bring about the installation of another emperor by the same guard.
After Caligula’s death, some of his images were removed or altered, but there is insufficient evidence that Claudius ordered every portrait and record destroyed. Suetonius even says Claudius declined to make the date of the assassination a public holiday, although it had brought him power. The Metropolitan Museum of Art’s record for a bronze portrait of Caligula discusses the removal and recarving of numerous imperial images. Some statues were altered to depict successors, while others survived in collections. The statues and the texts do not support the claim that Caligula’s memory was erased everywhere.
The familiar details of the assassination come from writers with different purposes. Suetonius preserves the insulting watchwords and incompatible versions of the sword strokes. Josephus builds an elaborate narrative around plotters who hoped to restore liberty; Dio depicts a cruel ruler meeting a gruesome end. A 2014 annotated study of Josephus’s account examines its value for reconstructing the succession and the possibility that he drew on Cluvius Rufus’s lost history. Such a connection would help explain his information without making him an eyewitness or rendering his speeches word-for-word records. They agree that Praetorian officers murdered Caligula, though they differ on motive and sequence. Claudius’s coin provides a fitting final piece of evidence: it celebrates the camp of the soldiers who secured his accession. The guard survived the emperor it failed to protect and provided the force behind the next ruler.
