Octavian Augustus established the Roman Empire and became its first emperor after a period of civil war. As emperor, he held several traditional Roman political offices and balanced power between the Senate, armies, and people. He rebuilt Rome and established a period of peace and prosperity known as the Pax Romana. The permanent forts established throughout the empire became Roman cities, helping to spread Roman culture. Augustus was succeeded by the Julio-Claudian emperors and then five good emperors who expanded the empire but also established the emperor's power to choose their successor based on merit rather than heredity.