How did Roman popular assemblies and tribunes represent democracy in Polybius’s analysis?

In his analysis of the Roman Republic, the Greek historian Polybius identified the Roman constitution as a prime example of a "mixed government," which he believed successfully balanced the three classic forms of political power: monarchy, aristocracy, and democracy.12

Polybius categorized the democratic element of the Roman system as being represented by the popular assemblies and the tribunes of the plebs. According to his framework, these institutions provided the necessary popular legitimacy and a check against the potential for tyranny or oligarchy. Specifically:2

• Popular Assemblies: Polybius viewed the various assemblies—such as the Concilium Plebis and the Comitia Tributa—as the democratic organs where the people exercised direct legislative, judicial, and electoral powers. He noted that these bodies allowed the citizenry to approve treaties and try high officials for misconduct.23
• Tribunes of the Plebs: Polybius saw the tribunes as the champions of the people, possessing the power to protect citizens from the arbitrary actions of other magistrates through their right of veto (intercessio).245

While Polybius admired this balance, modern scholars note that he likely exaggerated the symmetry of these checks and balances. In practice, the Senate maintained significant dominance, and the democratic elements were often influenced by aristocratic competition and patronage.12