Ancient Rome's governmental structure was a complex system that evolved from a monarchy to a republic and eventually to an imperial system, significantly influencing modern governance. The Roman Republic, established in 509 BCE, featured a mixed constitution with elements of democracy, oligarchy, and monarchy, which allowed for shared power among various branches of government. This intricate framework laid the groundwork for future political systems, including concepts like separation of powers and checks and balances that are evident in modern constitutions.