The Augustan Principate (31 BCE-160 CE)

Octavian's victory over Antony and Cleopatra ended a century of civil turmoil and decay.  When he returned to Rome in triumph in 29 B.C.E., everyone anxiously wondered how he would use his victory.  The Roman people and Senate heaped all sorts of honors on Octavian: triumphal parades, political offices, and titles, including that of Augustus ("revered one"), by which title he has been known ever since.
Augustus saw that there were two basic needs he had to satisfy in order to avoid the pitfalls of the past century. He saw two basic needs he had to satisfy.  For one thing, the civil wars and turmoil of the last century clearly showed the need for a strong one-man rule backed by the army.  Second, the traditional and conservative nature of the Romans made it mandatory that he make any reforms at least appear to be like the good old days of the Republic with its elections and many political offices.  Satisfying these two needs required a politician cleverer than Marius, Sulla, and even Caesar himself.  Luckily for Rome, it had such a man in Augustus who founded a new order known as the Principate after his honorary title of princeps (first citizen).
Augustus' solution was to take the army and law making powers and disguise them with harmless sounding Republican titles.  Out of all the Republican offices he took only two main offices, or more properly powers without the offices: those of tribune and proconsul (provincial governor).  Having special tribunician powers allowed him to propose laws to the Senate and assembly.  Being just a tribune, one of the humblest offices in Rome, made Augustus look like a man of the people and their protector.  However, his title of princeps gave him the right to speak first before all other officials instead of having to wait his turn like other tribunes.
Proconsular power gave Augustus all the strategically placed provinces with armies, thus giving his tribunician powers the clout to pass any laws he wished with a minimum of resistance.  In order not to appear too greedy, Augustus gave the Senate control of the non-military provinces.  In fact, one or two of these even had a legion with which the Senatorial governors could play soldier.  In such a way Augustus took effective control of the laws and army while leaving the Republic intact, at least on the surface.
Although his own position was secure, Augustus still had to provide for a smooth succession so his system would continue peacefully after he died.  He needed to appoint a successor much like a king would, but once again, make it look like the Republic.  He solved this with typical Augustan shrewdness by having his chosen successor assume the powers of tribune and proconsul while he was still alive.  Therefore, when Augustus died, the new emperor would already hold the important offices to guarantee a smooth transition of power.  Over time, and the memories of the Republic faded would fade and it would be taken for granted that the emperor's son or chosen successor should be the next emperor, even if he did not already hold the appropriate powers.
Once he had secured his own position, Augustus still had to provide for three things in order to rule the empire effectively: honest and efficient provincial governors, an honest and efficient bureaucracy to help them, and a loyal and efficient army to defend the frontiers instead of making trouble in Rome.  Augustus did two things to ensure honesty and efficiency in his governors.  For one thing, he paid officials regular salaries instead of leaving it up to them to make up for their own losses at the expense of the provincials.  This at least eliminated the more blatant need for corruption.  Augustus also had his own personal agents, called procurators, to keep an eye on officials in the provinces.  Any corrupt governors would be tried by the Senate.  However, it was unlikely that a governor's fellow senators would be so lenient with him as before, because Augustus kept a close eye on these proceedings to ensure justice.  Together, these reforms gave Augustus the efficient and honest governors he needed.
Augustus ensured more efficient governors by reviving the old cursus honorum (ladder of honors), whereby aspiring senatorial politicians would gain necessary experience and training by serving in the army and then holding a sequence of old Republican offices.  At the same time, it maintained the fiction of the Republic still carrying on by making good use of the old Republican offices.  Augustus obtained trained middle level officials from the rich business class of the Equites.  They had their own cursus honorum to go through before being eligible for various lucrative positions such as command of the fleet, Rome's grain supply and fire brigades, the Praetorian Guard (the emperor's own personal regiments), and the governorship of Egypt (kept as Augustus' private domain).
Augustus also needed trained bureaucrats to do the daily work of running the empire.  Previously, senatorial governors would take their friends and slaves to fill these positions, which led to all sorts of inefficiency and corruption.  Augustus replaced this system with a professional class of tax collectors and record keepers who held their jobs for extended periods.  He also ended tax farming, where the government auctioned off the right to collect the taxes.  This had been one of the worst sources of abuse under the Republic.  These reforms provided the provinces with an honest, efficient, and stable government.  There was also the need for trained people to fill many “middle-level” jobs, to oversee such things as the fleet, Rome’s grain supply, the emperor’s Praetorian Guard, and his new para-military fire brigade that doubled as a police force to keep order in Rome.   In this case, Augustus used the rich equites class, training them with a cursus honorum similar to that of the Senatorial class before they were eligible for these critical positions.
There were two issues to resolve with the army: its loyalty and expense.  In terms of loyalty, since Augustus' proconsular powers gave him control of the provinces and the armies within them, there was technically only one commanding general (imperator) of nearly all the Roman armies: himself.  Obviously, any emperor, especially a non military man like Augustus, would have to appoint men to lead at least some of the troops spread out along Rome's vast frontiers.  However, the troops stayed loyal to Augustus, not their immediate generals, for one good reason.  It was Augustus now, not the generals, who paid soldiers their regular pay and pension, generally with coins that bore the emperor's image as a constant reminder of who took care of the troops.  The central government, meaning Augustus, once again had control of its armies.  Occasionally, the troops would rediscover the fact that they held the key to power and would revolt to put their own generals on the throne.  For the most part, they stuck to the business of guarding the frontiers and left governing to the emperors in Rome.
Finally, in order to increase efficiency and cut costs, Augustus reduced the army from 60 legions to 28.  He generally placed these along the frontiers most threatened by invasion: the Rhine and Danube Rivers in the north and the Euphrates River in the east.  An equal number of auxiliaries (light infantry and cavalry) were also maintained there.  The total number of troops Rome had amounted to roughly 250-300,000 men defending an empire of possibly 50,000,000 people.  Such a small force for so large an empire had to be efficient.  The Roman legions during the Principate comprised the most tightly disciplined and efficient army of antiquity, and everyone knew it.  It was their reputation as much as their swords that defended the frontiers and gave the Mediterranean two centuries of peace.  Rome was also lucky in two ways at this time. First it faced no major threats on its borders.  Second, the Mediterranean, as the central geographic feature of the empire, allowed much faster communications and reaction time during emergencies.

The Empire after Augustus

Augustus died in 14 C.E., but his work lived on long afterwards.  For nearly two centuries afterward, the Roman world would experience peace such as it had never known before or since.  Its government was well trained, efficient, and honest, while its legions kept the frontiers and interior provinces secure.  Roman political history during this time is not very exciting, because relatively little happened besides a few palace scandals in Rome.
The empire expanded very little during this time, just rounding out its control of the Mediterranean and invading Britain.  Occasional wars would flare up in the East with the Parthians and in the north with various Germanic tribes, but there were no serious threats to the Empire.  The vast majority of people in the empire never experienced war and invasion.  Even the troops on the frontiers often saw so little action that they were kept busy and in shape by building the vast network of roads Rome is so famous for.  Peace and prosperity brought trade, both within the empire and beyond its borders with such exotic places as India and China far to the east.  Merchants traveled the legionary roads and the Mediterranean free from fear.  Peasants harvested their crops undisturbed by war.  And the legionary camps on the frontiers grew into permanent cities.
This was certainly a golden Age for civilization.  However, even times of peace and prosperity can carry within them the seeds of their own decay.  That was true of the Roman Empire in the second century C.E., although few if any people recognized the problems within their society.  At the same time, pressures were starting to mount against the northern frontiers.  Together, these internal problems and external pressures would combine to destroy the Roman Empire and begin the transition from the ancient world to the Middle Ages.