At the end of the 1989-90, fragments of a bronze decree started to appear on the antiquities market in Spain. The head of the local museum realised that something important had been discovered and set about reconstructing the find, in part by purchasing the remains. He then contacted some of the leading European experts in inscriptions. It became clear that that they had a startling find. of the decree relating to Piso were put together by 1999 [Latin text; image]. It is 176 complicated lines of Latin. The preservation of the decree is near perfect and it can be reconstructed with considerable confidence.

It begins with a date at which the decree was written, December 10th, and a list of witnesses to its writing. It records

1. Tiberius referral to the senate of the cases of
   • Cn Piso
   • M. Piso [his son]
   • Plancina
   • Members of the staff of Piso.
2.  The senate and Roman people expressed their gratitude that ‘they did not allow to be disturbed by the wicked plans of Cn Piso, the father, the tranquillity of the present situation of the republic, more than which nothing can be desired and which has fallen to us through the kind acts of of the princeps,  and then to Tiberius Caesar Augustus, our princeps, because he provided everything necessary for the discovery of the truth’.   The decree thanked Tiberius for his fairness and for acting judicially in response to the crimes and allowing a trial to take place and Piso to be defended, even though his guilt was so obvious that Piso eventually killed himself.

The emphasis is very much on peace and tranquillity. It is easy to overlook, but there is here an implicit threat: Tiberius might not have responded through a judicial process, but taken violent action against Piso, and possibly against those who supported him. Tiberius is being thanked for not launching a purge. 

3. The decree notes that the case was heard for several days and that many documents were produced that Germanicus had sent to Piso. These documents showed the remarkable constraint shown by Germanicus in the face of Piso’s provocations. The documentation showed that Germanicus suspected Piso of his murder. Piso had been sent as an ‘assistant’ to Germanicus Caesar, who had been sent by Tiberius’ authority in order to settle ‘overseas matters… which required the presence either of Tiberius Caesar Augustus himself or one of his two sons’. The actions of Piso ‘ignored the majesty of the August house, ignored even public law which granted powers to the proconsul [Germanicus] and indeed a proconsul whose appointment had been passed into law by the people, so that in whichever province he should enter, his power would be greater than whoever was proconsul in that province, excepting that in all matters Tiberius Caesar Augustus would have greater power than Germanicus Caesar’.

The decree notes the extensive authority given to Germanicus both from the authority of Tiberius and through the voting of a law that gave Germanicus this authority. The discussion here is notably legalistic. 

4. Piso ignored Germanicus’ authority and stirred up a war in Armenia and Parthia. He was bribed by Vonones of Armenia to allow him to escape and lead a rebellion in Armenia. He tried to raise civil war in Syria after the death of Germanicus, though war had long been ended by Augustus and Tiberius, with the result that Roman soldier was forced to fight Roman soldier.

These are the same charges as laid out in Tacitus. But they also show that the fear of the senators is civil war. 

5. Piso inflicted capital punishment on many without cause or trial and ‘crucified not only foreigners, but also a citizen centurion’. He corrupted the soldiers, giving them gifts from the treasury of the princeps under his own name, so that they divided into factions: Pisoniani and Caesariani.

Again, we see that the worry is civil war, but there is also a suggestion of tyranny and the failure of Piso to recognise the civil rights of citizens.

6. Piso rejoiced in the death of Germanicus and refused to engage in public mourning. He did not honour the memory of Augustus.

This large charge relates to the honouring of the imperial family. A failure to honour the imperial family would seem to throw into question the political stability of Rome. 

7. He was guilty and deserved yet more punishment that his suicide allowed. Further punishments include:

• No mourning for his death.
• His statues to be removed from display.
• His portrait mask is not to be displayed at funerals.
• His name removed from a statue of Germanicus on the Campus Martius (presumably he was one of the group of priests who paid for the statue).
• His property to be confiscated, except for land in Illyrium.

Such punishments are a condemnation of Piso’s memory. 

8. The senate were though mindful of clemency and decreed that

• The elder son of Piso (also Cn Piso) should have a half share in his father’s property.
• The elder son should change his praenomen (first name).
•  The younger son, Marcus, is forgiven and also allowed his share of the property.
• 1,000,000 sesterces to be given as a dowry to Cornelia, with 4,000,000 as her personal property.
• Structures that Piso had built over the Frontinal Gate be destroyed.
• Plancina is to be forgiven.
• The staff member of Piso were exiled and their property sold.

9. The senate asked Tiberius to end his period of grief and concentrate his hopes on Drusus. The senate praised the restraint of Livia and Drusus, commended Agrippina and Antonia, Livia (sister of Germanicus) and that the grief of Germanicus’ children and brother had been restrained. The senate also praised the devotion of the people and the equestrians, the fidelity of the soldiers, ‘who in most faithful piety cherished the Augustan house since they know that the safety of the empire was under the guardianship of that house.’

10 . The senate decreed that the speech of Tiberius be read out ans this decree inscribed in bronze in whatever places seemed best to Tiberius so that the memory of these events be preserved for future generations. The decree is to be inscribed in the busiest city of each province and in the winter quarters of each legion.The decree was passed by 301 senators, on December 10th, AD 20.

The wilder elements of the story are here lost: no poison or witchcraft. But we have here a distinctly different perspective from that of Tacitus. What worries the senators is the threat of civil violence. We have to remember that we are only six years into Tiberius’ reign. The threat is that the imperial family might have revenged themselves through extra-judicial violence and that Rome would once more face the horrors of civil war. Against that threat, the Roman senate, the people, the equestrians all stood firm. The inscription is a reinforcement of the unity of Rome under imperial authority. It is perhaps for that reason that it was so lavishly distributed and recorded.