What role did Augustus play in the history of the Roman Empire?

Answer this question in 1,200-2,000 words making a specific reference to the primary sources and visual aids:
The Greek historian of the Hellenistic Period Polybius asked: “Who is so thoughtless and lazy that he does not want to know in what way and with what kind of government the Romans in less than 53 years conquered the entire inhabited world and brought it under their rule–an achievement previously unheard of?”
With keen awareness Polybius realized that the Romans were achieving something unique in world history. What was that achievement? Clearly it was more than creating a huge empire. Despite frontier wars and provincial rebellions, how did the Romans maintain cohesion in the empire for so long? (You may want to discuss specifically the workings of the government, the mixed constitution, infrastructure, army, culture, economics, society, dates, etc.) Why did the Roman Republic come to an end? For the last third of the essay, evaluate the significance of the Roman Empire based on the readings. What role did Augustus play in the history of the Roman Empire? When did the Roman Empire reach its political and military high point? Why did it stop expanding in the East and in the North? You should make at least two references to primary sources found in the chapter in this paper. Do not write about events after 180 AD.