I was reading about the year of the 5 Emperors, and was intrigued by the preliminary Emperor, Pertinax, a man who had had a long successful military career, and seemed to have his head in the right place, increasing silver content in the currency.
As deeply influenced by the Romans and their culture and methods of war we are, we often wonder what would have happened had the Empire not fallen. This has given rise to a number of Timelines focused on various points of divergence. This timeline will not involve Rome to 2011 (or 2012), though it uses a PoD that was used, in the novel “Romanitas” to bring Rome to the modern era. However, I will have a fall of Rome, when the circumstances are right for such a thing. Rome was bound to fall someday, whether I like it or not. This fall may be entirely different, or in a different manner than the idea of a “fall” in many of your eyes, but that matters little. This will occur naturally, and as such I will never be planning more than 20 years into the timeline, in an attempt to keep the timeline fresh, and to keep it from seeming stale. This timeline will probably not include a full exploration of all topics, as that would be insane for a timeline.
Now, after I’ve scared off all you who would be afraid of such a strange and stale undertaking I will reveal the PoD, and the method I will be using. I am going from the reign of Pertinax, who, after some of the Praetorians revolted (in a sense of the word) and went to his palace to “have a little chat with him” was cut to bits, because he went and had a little chat with them. In this time, I am going to assume that he sends for the Equites Singulares Augusti, the faithful bodyguards of the Emperor (and the cavalry counterpart to the Praetorians,) to go and chop the revolting Praetorians into little bits.
The butterfly style I will be using for this TL will be moderate. Some changes will have resulted in chains of changes that resulted in zero divergence, while others will have major divergence. However, geography will still be important in this TL, because this must be reasonable. I will not have random wanky expansionism, no matter how fun it is. Now that’s all over, why don’t I actually begin. Additionally I will be using OTL dates (November, AD, etc.) rather than Roman, because it just gets wacky after a while.
BTW: Actual content will be in Times New Roman, Authors Notes, Prefaces, etc. will be in standard font.
[Pertinax]

[OTL SECTION]
The Emperor Pertinax took power immediately following the reign of the debauched and insane Commodus, son of the philosopher-king Marcus Aurelius. After a palace conspiracy, which may or may not have involved the future emperor himself, the chief conspirators went to the ornate mansion of Pertinax, where on the 31st of December 192 AD, they offered him the position of Emperor. After a long night of preparation, the following morning, he went to the Castra Praetoria, and was proclaimed Emperor.
Attempting to adopt moderate ruling policies, Pertinax was frustrated in many regards by the Praetorians, who, enraged by his reluctance to pay them the traditional bonus they received upon the ascension of a new Emperor. Eventually, convinced by their rhetoric (ability to kill and overthrow him) he relented, and sold off the estates and sex slaves of Commodus, though many rumors say he bought a good deal of those for himself.
In March of that year, after setting down several currency reforms designed to curb inflation, he was the victim of an attempted coup whilst inspecting arrangements for the grain handouts in Ostia. When he returned to Rome, the ringleaders were executed, and the attempted Emperor, the Consul, Quintus Sosius Falco, was pardoned. Later in March, after receiving either less of the promised pay, or being displeased at the failure of the coup earlier, late at night 300 of the Praetorian Guard, armed only with their blades, were allowed into the courtyard of the palace, intent on killing the Emperor and placing one more favorable to their interests on the throne.
[Praetorians] 
Pertinax refused to come out of the palace, (PoD) instead sending an envoy to declare them as acting against their interests, as well as those of the State and of the Gods, and thus rebels. At that point, the Equites Singulares Augusti, who had been roused earlier in the night after reports of the Praetorians entering the palace reached them, charged into the mass of unarmored Praetorians, killing them all within a very short period of time.
Immediately afterwards, Pertinax sent the Imperial Cavalry to the Castra Praetoria, where the faithful bodyguards of the Emperor killed nearly a thousand of the Praetorian Guard before they could even attempt to resist. By the end of the next day, most of the Praetorian Guard was dead or captured, and the Emperor declared them enemies of the state, and had the living ones deported to mine the rest of their days away in Spain.
Soon afterwards the Praetorian Guard was disbanded permanently, with lasting consequences for the state, and no new bodyguard was devised. Lacking entirely a full replacement for the Praetorian Guard, it would be nearly 5 years before such a thing would occur.
The policies of Pertinax were distinctly senatorial, as he had been a significant member of that body, and derived much support from them as well. Later in the year 193, towards late September, he removed the idea of “Equestrian” provinces. Henceforth all political power was concentrated within the millionaire senators, and all senatorial power was derived from the Emperor, largely by concentrating all power within his own person, a strategy which had been used to greater effect by Emperors such as Augustus before him.
Through much division of power, by the end of the year 193, Pertinax was reasonably secure in his throne, enough to finally implement the fiscal reforms that he had been planning. The silver content and gold content of coins was significantly increased, and agricultural reforms (which in OTL had been proposed) were implemented, giving fallow land the ability to be plowed and used by whomever should occupy it. This reform largely benefited the large scale landowners, who had the power to enforce their control of the land, and lead to much servitude by lower classes, an unintended effect.

In 195, after roughly three full years in power, Pertinax died, at the age of 69, in his sleep. His son, Publius Helvius Pertinax, who was eleven at the time, succeeded him, having been nominated as "Caesar" two months before, under the regentship of a former general and personal friend of Pertinax, Didius Julianus, who had served with the dead Emperor as join Consuls under Marcus Aurelius.
The regent soon proved to be fond of his power, leading several futile raiding expeditions out of Dacia to pacify and subjugate unruly barbarians, cutting a swathe all the way to the Rhine both times. These raids did little, though they did endow the young Emperor with a love of martial affairs.
The Emperor accompanied the regent on these expeditions, after he reached the age of thirteen, proving to be a capable commander, as he defended the armies rearguard very ably after a German ambush just north of the Agri Decumates, as well as leading many other minor raids north of the border. These never involved enough troops to be quantified as a campaign, nor were they minor enough to not go down in the records, as they involved both possessors of Imperial Power.
Didius Julianus, however, proved weak in comparison to the senatorial forces that wanted to give the Emperor independence, in the hopes that he would prove susceptible to Senatorial prodding, rather than by the Regent. The Senators feared the development of new powerful Emperors not sympathetic to their cause, unlike Pertinax, and so attempted to free the Emperor from his regent.
At the earliest possible occurrence, when the Emperor was sixteen, the Regent was slain while touring the Forum, in a large-scale senatorial conspiracy. It is said that over twenty participated, each sinking a dagger into the Regent in an orderly manner.
Brash with youth, Publius Helvius Pertinax, who took the cognomen “Getis,” after his victories over many tribes of that area, had twenty senators arrested, and their estates confiscated after their death. This had the effect of placing the Emperor between camps pro-Regency, and pro-Senatorial dominance, as he attempted to consolidate his own personal power. However, afterwards, he placated the Senate with much conciliatory speechmaking, and announced his intention to lead an attack upon Parthia, in which he promised much glory would be had for all involved, in an attempt to secure his reign.
Before he left for his new campaign, Getis replaced the Praetorians finally, though he attempted to create a system to guard the Emperor with personal friends, as well as prevent the single united front the Praetorians had controlled before. Taking inspiration from Alexander the Great, whom he idolized, though he also acknowledged his shortcomings, Getis created a system where ten “Companions,” selected by each Emperor, commanded individual cohorts of the guards. Though this system was relatively short lived, it provided a durable Imperial bodyguard for a major period of Roman history, and one that did not have a tendency to play kingmaker.
In May of 200, Getis set out with a force of five legions, plus the ten cohorts of 500 that formed his bodyguard, towards Armenia, claiming that the king, long a Roman client, had betrayed the Romans for Parthian dominance. Regardless of the veracity of this statement, soon the Romans had occupied Armenia and the surrounding territory, all the way to the Caspian Sea, reaching what was effectively the edge of the Roman world.

By June, the campaigning season had largely ended, as only minor skirmishes continued along the border with Parthia. These began to escalate, until, in mid September, Getis marched into Parthian soil, apparently emulating Trajan, as he followed the course of the Tigris down to Ctesiphon, where, after a month long siege, was sacked in October, after the gates were betrayed. The city was almost depopulated, as the entire fit population, male and female, was marched away in chains, leaving only elderly and children.
The Romans knew they could not hold on to Mesopotamia, however, and so, by November sued for peace. Parthia, knowing they were not in a position to fight, due to harassment on borders both in Central Asia and in the Near East ceded all attempts to control Armenia, and gave some minor Mesopotamian territorial concessions. Leaving two of his legions in the region, Getis returned to Rome by mid December, where he celebrated a triumph against the Armenians and Parthians, taking the Parthian king’s throne and dragging it along the back of two chariots, before melting it down and donating it to the urban poor. (Actually, the throne itself provided little of the gold, with most of it coming from the remnants of the estates of the executed senators)
Soon, Getis would embark on yet more military campaigns, but for now, the Emperor contented himself with ruling his newly expanded Empire from his palace, and reveling in the power that his Empire, the greatest the world had ever seen, possessed.