Fall of Sejanus (AD 31): Tiberius Destroys His Favourite

The fall of Sejanus was the sudden destruction of Lucius Aelius Sejanus, the commander of the Praetorian Guard and the most powerful man in Rome under the emperor Tiberius, on 18 October AD 31. Summoned to the Senate expecting new honours, he heard a letter from Tiberius denouncing him and was executed the same day. His fall exposed the danger of the emperor’s bodyguard commander and set off years of treason trials.

The rise of Sejanus

Sejanus was born around 20 BC at Volsinii in Etruria, into a family of equestrian rank, the class below senators. In AD 14, when Tiberius succeeded Augustus, Sejanus became joint commander of the Praetorian Guard with his father, Lucius Seius Strabo. When his father was made prefect of Egypt, Sejanus took sole command.

He strengthened his position by concentrating the guard’s nine cohorts, estimated at between about 4,500 and 9,000 men, in a single fortified camp, the Castra Praetoria, on the edge of Rome around AD 23. Tiberius, a reserved and suspicious ruler, came to trust him deeply and called him a partner in his labours.

In AD 23 Tiberius’s son and heir Drusus died. Sejanus then turned against the family of the late Germanicus, Tiberius’s nephew and adopted son: his widow Agrippina the Elder and her sons Nero Caesar and Drusus Caesar, who were next in line. In AD 25 Sejanus asked to marry Livilla, Drusus’s widow, but Tiberius refused.

Power in the emperor’s absence

In AD 26 Tiberius left Rome for Campania, and from AD 27 he lived mostly on the island of Capri, in the clifftop Villa Jovis. He never returned to the city. Sejanus controlled access to the emperor and the flow of information to him, and senators competed for his favour.

With Sejanus’s encouragement, Agrippina and her eldest son Nero Caesar were declared public enemies and exiled in AD 29; Drusus Caesar was imprisoned in AD 30. All three later died in captivity. In AD 31 Sejanus held the consulship together with Tiberius, a high honour for a man of equestrian birth, and there were signs that he might be allowed to marry into the imperial family.

The letter of 18 October AD 31

Tiberius’s attitude changed during AD 31, for reasons that remain unclear. The Jewish historian Josephus says that Antonia, the mother of Germanicus and grandmother of the surviving heir Gaius (Caligula), sent a warning letter to Capri. Tiberius may also have feared that Sejanus would harm Gaius, whom he had begun to favour.

Tiberius planned with great care. He secretly appointed Naevius Sutorius Macro as the new Praetorian Prefect. On 18 October Macro arrived in Rome, told Sejanus that he would be granted the tribunician power, a sign that he was marked as a successor, and sent him into a Senate meeting at the Temple of Apollo on the Palatine. Macro then dismissed the guards on duty, replaced them with men of the city watch and went to the Praetorian camp to take command.

In the Senate, a long, rambling letter from Tiberius was read. It ended with an order to punish two of Sejanus’s associates and to arrest Sejanus himself. Senators who had courted him moments earlier abandoned him. He was taken to the state prison and executed that evening, and the crowd attacked his statues. His body was thrown down the Gemonian Stairs, the place where executed criminals were displayed, and after three days cast into the Tiber.

Purges and aftermath

Sejanus’s children were executed in the following weeks. His former wife Apicata, before taking her own life, wrote to Tiberius claiming that Sejanus and Livilla had poisoned Drusus eight years earlier. Livilla died soon after, according to Cassius Dio starved to death by her mother Antonia. Treason trials against Sejanus’s friends and supporters continued for years and cost many lives.

Macro became the dominant figure in Rome. When Tiberius died in AD 37, Macro helped Caligula to the throne, but the new emperor forced him to suicide the following year. The role of the Praetorian Guard in making and breaking rulers continued, most dramatically in the assassination of Caligula in AD 41.

Sources and legacy

The main surviving account is by Cassius Dio, writing two centuries later. The relevant part of Tacitus’s Annals is lost, although his narrative of Sejanus’s rise survives and portrays him as a ruthless schemer. Juvenal’s tenth Satire uses Sejanus’s statues being melted down as an image of how quickly fortune turns. In 1603 Ben Jonson’s tragedy Sejanus His Fall brought the story to the English stage.

Timeline

• AD 14: Sejanus becomes joint Praetorian Prefect with his father.
• c. AD 23: The Praetorian Guard is concentrated in the Castra Praetoria.
• AD 23, 14 September: Tiberius’s son Drusus dies.
• AD 26-27: Tiberius leaves Rome and settles on Capri.
• AD 29: Agrippina the Elder and Nero Caesar are exiled.
• AD 31, January: Sejanus becomes consul alongside Tiberius.
• AD 31, 18 October: Sejanus is denounced in the Senate and executed.
• AD 37, 16 March: Tiberius dies; Caligula succeeds with Macro’s help.

Why it matters

The fall of Sejanus showed both the danger and the dependence at the heart of the Roman imperial system. An emperor who withdrew from Rome had to rely on a deputy, but a commander of the guard with too much power could threaten the throne. The episode left a lasting image of the favourite who rises too high and falls overnight.