Pax Romana: The Reign of Augustus in 400 words.
"It was the will of our ancestors that the gateway of Janus Quirinus should be shut when victories had secured peace by land and sea throughout the whole empire of the Roman people; from the foundation of the city down to my birth, tradition records that it was shut only twice, but while I was the leading citizen the senate resolved that it should be shut on three occasions." -from Res gestae divi Augusti.
He invented the office of Roman Emperor. He exploited the conditions of civil strife that were rampant in his youth. He consolidated his power. He standardized the pay and role of the soldier in the Roman world. He obsessed over kings:
"…he had the sarcophagus containing Alexander the Great…removed from its shrine… (and) showed his veneration by crowning the head with a golden diadem and strewing flowers on the trunk. When asked ‘Would you now like to visit the Mausoleum of the Ptolemies?’ he replied: ‘I came to see a King, not a row of corpses" (from Suetonius)
and commoners alike:
"During his consulships, he usually went on foot through the streets of Rome… His morning audiences were open to commoners as well as… senators…" (from Suetonius).
Roman history is filled with exploiters of civil strife (Julius Caesar) and public opinion (Tiberius Gracchus). It is peppered with conquerors (Pompey) and administrators (Gaius Gracchus). There had even been precedents set for centralization of power (Sulla for example). But the defining message of Augustus’ reign was the Ara Pacis Augustae, the altar of the Augustan Peace. It was not his exploitation of civil war that made him unique, but rather his exploitation of civil peace. The Altar of his peace symbolized a condition that allowed Rome to be "clothed in marble"; the Aeneid to be written; the city to flourish; but most importantly it allowed the monarchy he forged amidst chaos to live on hundreds of years beyond his death. He was a man that did many common things, but peace in an empire is an uncommon thing and it was that thing that made him Emperor.
Beyond that all other questions are trivial. Rome’s collapse can no more be blamed on the powerful monarchy that he forged than on the ill-equipped republic that preceded it. When he found it, Rome was like the senator Cerrinus Gallus, at war with itself, blind, prepared to die. Augustus "spoke so consolingly to it that it changed its mind" (from Suetonius). The life of one man is as valuable as an empire: both incalculable, irreplaceable. Augustus saved them both from themselves. Who can weigh the costs against the reward? Who can know what might have been? All we know is what was: the doors of the temple of Janus were shut three times.