After the Republic, the Roman Empire transitioned to an imperial form of government, characterized by the centralization of power under a single emperor. The shift began in earnest with the rise of Augustus (Octavian) as the first Roman emperor after the fall of the Republic in 27 BCE. This transformation marked the end of political institutions like the Senate's significant authority and initiated an era of autocratic rule. Augustus implemented reforms that stabilized and expanded the empire, leading to a period known as the Pax Romana. This change fundamentally altered governance in Rome, influencing political structures in many subsequent civilizations.