According to Aristotelian political theory, each form of government had its merits but inevitably devolved into its most oppressive incarnation until it was overthrown. Thus a monarchy would become a tyranny, only to be overthrown by an enlightened aristocracy, which slid to repressive oligarchy until popular democracy overwhelmed the oligarchs, opening the door for anarchy, and so back to the stabilizing hand of monarchy again. Polybius believed the Romans had beaten this cycle and could thus keep growing when other cities collapsed under the shifting sands of their own inadequate political systems.23
The monarchical element of the Roman constitution was the executive consuls. Thanks to the Roman aversion to kings, the Republic did not have a single executive and instead elected a pair of consuls who would share supreme military, political, and religious authority. To limit the risk of a tyrannical power grab, each executive partner had the ability to veto the decisions of his colleague. But even more importantly, the term of office was just a single year. At the end of their year in office, the consuls would return to the ranks of the citizen body and a new pair of leaders would replace them.24
The practical Romans, however, did create an emergency office called the Dictatorship. In times of crisis, the consuls could pass power to a single man who would hold absolute power in order to deliver Rome from danger. And this did not just mean foreign threats: the first dictator was appointed due to plebeian unrest in Rome rather than threat from a hostile neighbor. But, critically, the Dictatorship expired after six months. As the Romans held an implacable hatred of kings, the Senate authorized any citizen, at any time, to kill another citizen caught seeking regal power. For nearly five hundred years Roman dictators never failed to lay down their power.25
The aristocratic element was, of course, the Senate. Originally one hundred old men organized by Romulus to act as a council of state, the Senate numbered about three hundred old men in Polybius’s age. Drawing its members from the richest and most powerful families in Rome, the Senate had evolved into the central political institution of the Republic. With the Senate composed of former magistrates, it served as the principal adviser for the annually elected leaders. Rarely did consuls pursue a policy without the Senate’s deliberative input.26
Finally, the democratic element was found in the Assemblies, which were open to all Roman citizens. By the time of Polybius there were three principal Assemblies: the Centuriate Assembly, which elected senior magistrates; the Tribal Assembly, which elected junior magistrates, passed laws, and rendered legal judgment; and the Plebeian Assembly, which had many of the same powers as the Tribal Assembly but which elected the tribunes and were open only to men of plebeian birth. The democratic element of the Roman constitution is often underrated, but the Assemblies were incredibly powerful. Only an Assembly could enact a law or pass capital sentence on a citizen. And while a citizen could always appeal a verdict
In Polybius’s construction, the three elements of the Roman constitution existed in a balance that prevented any one element from dominating. But though Polybius was a gifted theorist, by the time he was writing his history in the mid-100s the balance he admired had already been disrupted. The Senate had emerged from the Punic Wars stronger than it had been since the First Secession of the Plebs in the 400s. During the Punic Wars the annual changeover of senior military commanders became a hindrance to war planning and the Senate collectively began to take the lead in developing and executing policy. The senators also became adept at ensuring subservient clients were elected tribunes. By the end of the Punic Wars the consuls, the tribunes, and Assemblies no longer acted as a check on the Senate, but as an extension of it. Even as Polybius wrote his paean to Roman constitutional balance, the senatorial aristocracy was sliding into repressive oligarchy.28
