The trial of Piso is the next great set-piece in the account of Tiberius’ reign. We have an extended account in Tacitus, which until recently gave us much of our information. In the late 1980s fragments and a near complete copy of a long decree passed by the senate on the conclusion of the trial in late December AD 20 appeared in the Spanish province of Baetica. This is the text known as the Senatus Consultum de Cn Pisone Patre [the decree of the senate on Cn Piso the father] (See here for an account of its publication). We start with the account in Tacitus and then turn to the inscription.

Piso Comes to Rome

After the fiasco of his failed attempt to suborn the troops and re-secure his province in Syria, Piso made very slow progress back to Rome. He was not under arrest. He had not been charged with anything. Rome lacked a police force, but it the emperor needed anybody secured, he sent the praetorians. But Piso wandered back under his own authority (Annales 3.8-9).

He sent his son (the younger Piso) to meet Drusus, who was about to head out to command troops in the northern Balkans. In dynastic terms, Drusus was the beneficiary of Germanicus’ death since the two were the most obvious successors to Tiberius.  Piso was or had been close to the imperial family, especially Livia and Tiberius and he may have been hoping for some measure of support. But Drusus and Germanicus appear to have been close and the younger Piso was rebuffed.

Eventually, Piso landed at Ancona and made his way across Italy. He met a legion and attempted to ingratiate himself. It was not clear what he was doing.

• Was he trying to show that he had popular support?
• Was he showing confidence?

His arrival in Rome was full of pomp. He and his wife Plancina sailed in during the day and disembarked with a crowd of attendants. He celebrated his return by holding a feast at his home. In Rome, those facing trial often put on mourning and went round the city finding friends and eliciting sympathy.

• Was he showing his importance?
• Was he reminding people that he was a great man in the Republican tradition?
• Was he pretending that he did not know what was coming next?

His enemies were gathered and competing to be the one that brought him down and revenged the loss of Germanicus.

The Trial (Annales 3.10-19)

Senators were tried were before their peers. On the day after Piso’s return, there was an application to bring a prosecution. This caused an argument as to who had the most moral authority to lead the prosecution. The first accuser gave way, but obtained the right to bring a prosecution against Piso for his behaviour earlier in his career. This was not an unusual development in political trials: once someone tried to strike down an enemy through legal action, all their career was subject to critique (or praise).

But the matter was delicate: Piso was well-connected and the matter touched the imperial house. The senate suggested that Tiberius might hear the case himself. Tiberius considered with his advisers: was it better to deal with the matter quietly or openly?

He sent the case back to the senators. Drusus came back from Illyria: it was winter and there was no campaigning, but it seems likely that he wanted to be present for the trial.

Piso sought leading men in the senate to speak for him. Many refused, but he did gather a team, including his brother, Lucius Piso.

The trial opened with old accusations about Cn Piso’s corruption in Spain. It then focused on events in Syria. The claims were that he had suborned the troops, launched a civil war, attacked (been savage towards) the friends of Germanicus [whatever that means], poisoned and employed sorcery against Germanicus, leading to his death. Piso and Plancina were associated with a ‘notorious’ poisoner called Martina, who had died, conveniently, while under arrest.

Some of these accusations simply collapsed. The senators demanded a certain level of proof before they condemned one of their one and Piso was a powerful and well-connected individual. But he could not deny that he had raised the troops against Germanicus’ friends.

The mood was now ugly. There were popular demonstrations against Piso. Statues of Piso were being broken. There were threats of violence. At the end of the day, Piso had to be sent home with a military escort.

Ultimately, the result was not in doubt. The friends of Germanicus were implacable. The evidence of raising troops against their commanders was incontrovertible. Tiberius and Drusus were not going to intervene to save someone who had been so evidently hostile towards Germanicus.

Plancina, whose friendship with Livia was close, started to negotiate on her own behalf. Late at night, Piso ordered the doors closed in his room. He was found dead the next morning, his throat cut.

Loose Ends

Tacitus recounts rumours that Piso was murdered. He had, it was claimed, a letter from Tiberius that would have justified his actions. The document was waved about, supposedly, but never read from. It disappeared. Tiberius felt that the death reflected badly on him. But he found a suicide note that had a plea for clemency towards his son, who had been under the authority of his father and thus had had no choice, but failed to mention Plancina.

The son was punished by exile and loss of property, but escaped with his life. Tiberius made good his losses. Plancina was spared.

The senate voted honours to Tiberius, Livia, Antonia, Drusus, and Agrippina. There was some debate as to whether Claudius should be include. His name was added. Coins were issued proclaiming the triumph of justice. We get more detail in the senatorial decree, which broadly confirms the Tacitean account.

Coin of c. AD 22 issued by the senate and proclaiming Iustitia (Justice). Yale University Art Gallery

Conclusion and Questions

What was at stake here?

At one level, the story is one of imperial power and revenge. Piso was punished for his arrogance in threatening imperial power. But his behaviour is puzzling. Was he really a remnant of the Republican age, incapable of surviving in the new imperial politics?

He was closely connected to Tiberius and this is a consistent element in his presentation.

• Did he see himself as a check on Germanicus?
• Did he perceive himself as doing Tiberius’ will?
• Did he have a document to that effect?

Why were the family rewarded? It seems to me that the public rewards would seem to reflect a view that Piso’s acts were a threat to civic peace. Removing him was thus an act of civic virtue.

• Why was Plancina forgiven?

In the Tacitean account, Piso’s death is managed by Sejanus, the praetorian prefect. His sinister presence points to some of the themes of the next chapter of Tiberius’ reign.

Tiberius               Germanicus         The Rise of Sejanus            Senatus Consultum de Cn Pisone Patre