The death of Germanicus and subsequent trial of Piso produced the gravest conflict that Rome had seen since the civil wars. After the Battle of Actium, Augustus had methodically fought to consolidate the power of Rome in his own hands. He established his autocratic position, designated princeps by the Senate, upon the idea that his ascension to power would quell the infighting that had ravaged Rome in the years before his reign. Despite his efforts, the Augustan Principate was not a panacea. Piso’s trial gives the best evidence that Augustus’ political order was not as stable as it appeared. The legitimacy of the princeps and the powers of imperium maius were called into question. Deep concern in Rome that loyalty to the princeps had been ruptured can be seen in the Senate’s decree on the trial, the Senatus Consultum de Pisone Patre. The Senate knew that the tinderbox of factionalism had been lit once again and other provincial governors could possibly follow in the footsteps of Piso. This decree captures their apprehension towards a resurgence of infighting and their anxiety to present themselves as the undisputed governing body of Rome. Ultimately, it affirms that peace in Rome was impossible without a strong, central political position that controlled the loyalty of the Republic.
Augustus connects the princeps to peace in Rome in the Res Gestae. His view of Roman peace can be seen when he says, “I successfully championed the liberty of the republic when it was oppressed by the tyranny of a faction” (Augustus Res Gestae 1). This vision of peace is one where Rome is free of internal conflict fueled by factionalism. Augustus considered autocratic rule the best route to peace because a strong, central figure could wield enough influence to stop factionalism from reemerging. He deftly accrued power in Rome without destroying its Republican institutions through various methods. One was by refusing “the dictatorship  offered to [him] by both senate and people” and the consulship every time that it was offered to him (Augustus Res Gestae 5). This meant that is technically was the Senate who gave him power despite his “refusal” to take it on his own. Self-deification was the method that allowed Augustus’ power to continue past his death. The Senate deified Augustus “against” his wishes in the same way that it gave him the powers of imperium maius. For example, he writes that he initially “declined to be made pontifex maximus” until he “received this priesthood” during another consulship (Augustus Res Gestae 10). The Senate’s legitimacy remained intact because they gave Augustus his autocratic powers. His hold on this power allowed him to keep the Republic free from the factionalism that he had designated as its existential threat. Thus the idea of peace, in practice or in principle, was inherent in the position of the princeps.
The Senate’s treatment of Tiberius in the Senatus Consultum de Pisone Patre elucidates the political importance of peace to Rome during Piso’s trial. At the beginning of the decree, it says:
THAT the Senate and Roman people, before all else, expressed gratitude to the immortal gods because they did not allow the tranquility of the present state of the republic — than which nothing better can be desired and which it has fallen to our lot to enjoy by the favor of our princeps (Senate SCdPP 10-15).
The “immortal gods” and “our princeps” are presented as the arbiters of the peace of the Roman Republic; their power to take away peace if they so desire is subtly implied. This makes Piso’s defiance towards the princeps dangerous because it threatens the retractable peace that has been given to Rome. He is characterized by the Senate as someone “who also tried to stir up civil war (though all the evils of civil war had long since been laid to rest by the divine will of the deified Augustus and the virtues of Ti. Caesar Augustus)” (Senate SCdPP 45-50). Civil wars are labeled as evil by the Senate because the main purpose of the Augustan political order had been to prevent them. The Senate interpreted Piso’s actions as an assault on the hearts of the Roman state: its peace and the Principate. Their interpretation is made clear at the end of the decree when they write that “the safety of [their] empire had been placed,” in the “custody” of the house of Augustus (Senate SCdPP 160-165). Piso’s attempt to incite civil war is the attack on peace; the fact that peace had been established and maintained by Augustus and Tiberius meant that he had attacked the Principate as well. Peace is treated with such importance because the Senate knows that it is the fabric that holds the Roman state together. Without peace, Rome could not exist.
Rome’s dependence on the princeps for peace is also important in showing the importance of an idea in holding the Republic together. It is vital to recognize that the title of princeps is something that the Senate gave to Augustus. This was revolutionary because it meant that the Senate created an idea of what the princeps was meant to be in addition to Augustus’ thoughts on the position and the actions he took while occupying it. To say that the idea of having a central political position to keep the peace was sufficient to achieve it would be disingenuous to the efforts of the emperors. However, the Senate’s defense of the position, rather than a defense of the man who occupied it, suggests that the role and significance of the princeps transcended all else. Perhaps the new Roman Republic was founded upon an idea as much as it was founded upon the efforts of one man.