An account of the fall of the Roman Republic does not record the events of a day, a few months, a year, or even a decade. The history of the fall of the Roman Republic covers over a hundred years of political events. The Roman Republic, as Polybius had recognized, was certainly a durable form. It was not going to be toppled by a single coup or spontaneous riot. Indeed, ancient Rome had many dramatic moments in its history—just read the histories of Livy, Sallust, Tacitus, or Polybius. But ancient Rome also had stability. Centuries of political stability, in which the Romans built up political customs and civic traditions—the honored mos maiorum (the tradition of the ancestors). The fall of the Roman Republic is in many ways the story of how the Romans strayed from these customs little by little and failed to create solutions to perennial problems, while too frequently pursuing private gain rather than the common good.

The political upheaval that resulted in the fall of the Roman Republic began in 133 BCE with the murder of the tribune Tiberius Gracchus, about whom more will be said in Chapter 5. Though his murder was a dramatic event that left a strong impression among those who lived through it, the event itself at the time probably did not feel like a harbinger of the end of the Roman political system. In some ways, it was one event that could be isolated in time. Yet it was a watershed event because it changed the idea of what was acceptable in Roman political life, specifically the use of violence. This change in how the Romans related to one another resulted in further violence and greater transgression of the accepted norms of political behavior, such as magistrates holding office for more than one year at a time, citizens rioting in the assemblies, and generals marching armies on Rome. The Romans had not done these things before, or if they had done them, they quickly found them unacceptable. After 133 BCE, the Romans would find such stark violations of their republican traditions increasingly acceptable. Yet each violation could be seen at the time merely as an exception to the norm rather than the new precedent it frequently became. Many examples of this process, transgression of accepted norm becoming later precedent, will be cited throughout the following chapters.