The Roman government transitioned from a monarchy to a republic in 509 BCE when the last Roman king, Tarquin the Proud, was overthrown. According to tradition, Tarquin was a tyrannical ruler who abused his power and disregarded the rights of the Roman citizens. This led to a rebellion led by a group of powerful noble families known as the patricians. They successfully drove out Tarquin and established a new republican system of government.
The change to a republic marked a significant turning point in Roman history and laid the foundation for the Roman state's future rise to prominence. The republican government was characterized by the distribution of power among different institutions and offices, including the Senate, the Consuls, and the People's Assemblies, which provided checks and balances to prevent any single individual from accumulating excessive authority. This system was aimed at ensuring greater accountability, public participation, and the protection of citizens' rights and liberties.