Octavian defeated Marc Antony and Cleopatra to become Rome's first emperor, initiating a period of peace and prosperity known as Pax Romana. Under Octavian, renamed Augustus, Rome experienced over 200 years of stability through expanded trade, cultural blending with Greece, and engineering projects. Good emperors like Trajan and Hadrian expanded the empire's borders while others like Marcus Aurelius were philosopher-soldiers, but Commodus' disastrous rule marked the decline of the Pax Romana period.