It is important to know why the conspirators, most of them Senators, hated Commodus and chose Pertinax. They were from the "optimati" faction, the self-proclaimed "best people". Commodus was certainly an egomaniacal nut case, but the Senate was used to dealing with that. No, they hated Commodus because he had ensured his domination over the Senate by appealing directly to the "populares" (the people, that is, everybody who was not "optimati") by giving them cash and elaborate games in the arena. Commodus had also fortified the northern border of the Empire and then brought the troops home from the long wars in the north, and that greatly decreased the incomes of Roman war profiteers, those same Senatorial "optimati." Commodus was beloved by the people and the army ranks (he was probably the second most popular Emperor ever, only behind Augustus Caesar) and hated by the military-industrial complex.

Publius Helvius Pertinax was a different pot of garum. He was a military professional and so could be expected to send the armies back into the field. Although not from a Senatorial family, he had worked his way through the army from a sub-lieutenancy to legionary commander and was made a senator as a reward for his successful military campaigning as one of the top generals in the army of Marcus Aurelius, the father of Commodus. Although they are not documented, he probably made promises to his fellow conspirators.

Pertinax was actually the son of a former slave, who had made a fortune as a commodity trader (timber or wool -- stories vary) and who probably sold supplies to the army, everybody's biggest customer. According to historical accounts (probably made up later) his father named him Pertinax to memorialize the father's perseverance in rising from slavery to business success. It was more likely, that Pertinax picked up the nickname later and it referred to stubbornness. Pertinax got a good classical education and for a number of years was a teacher. At age 35, dissatisfied with teachers' wages, he decided to enter the army officer corps. He probably had good connections through former students and their parents and rose quickly through the ranks. Like other Roman military success stories, he moved easily between civilian and military postings and had command of one of Marcus Aurelius's legions along the Danube. Other important military commands followed. But the northern wars ended when Marcus Aurelius died of natural causes in 182 AD in a Danube military camp. The army rank structure started to tighten up, and there were fewer promotions and commands available. Commodus also clearly wanted to close out wars on the other frontiers, and, although the lower ranks of the military and the subalterns relished their return to Rome, Pertinax and the other generals were not happy with fewer wars and conquests to make their names and line their pockets,

In short order, plotting to remove Commodus began, and Pertinax was in the thick of it. The plot of 182 failed, because at least one of the conspirators was a Commodus spy. Although Pertinax was clearly implicated, the merciful Emperor pardoned him with most of the others involved. Pertinax's career suffered for a short time, but he was one of the army's best generals, and so he was called up again to suppress a revolt in Britain, an assignment which, not incidentally, also sent him far from the Roman political scene. Other commands followed, which won back the Emperor's confidence, and he was back in Rome in time for the second conspiracy.

It was only a short time after his accession that Pertinax realized that there was less money in the treasury than he had anticipated -- Commodus had spent less on military campaigns, but then he gave the savings to the "populares" as cash gifts or spent it on games. Corners had to be cut, and one of them was the size of the "gift" that Perinax had promised to the Praetorians for their cooperation in putting him into power. Pertinax tried to put a positive spin on the cut, but the Praetorians would rather have seen savings made elsewhere. While Pertinax was down in Ostia inspecting Rome's grain supply, Laetus, a former ally of Pertinax in the plot to kill Commodus, now conspired with the Praetorians to oust Pertinax. Pertinax got wind of the plot and rushed back to Rome where he addressed the Senate, saying that it was the fault of palace freedmen that the treasury cupboard was bare and that the Praetorians were attempting a coup. Senator Falco whom the Praetorians had wanted to raise in place of Pertinax, was pardoned by Pertinax and quickly went into retirement. (He showed up as one of the "good guys", the senatorial plotters against Commodus, in the Gladiator movie.)

In his speech before the Senate, Pertinax made the mistake of claiming that he had paid the Praetorians in full the customary "donative" -- simply not true -- and that falsehood led to even more discontent in the Praetorian ranks. Laetus was left in place, his part apparently undiscovered. Laetus then appears to have had several praetorian plotters executed, saying that it was done on orders of Pertinax.

On March 28, 183 AD, about 200 armed Praetorians entered the Palace. The freedmen, who could have barred the doors, were not willing to protect the Emperor after the insult in the Senate. Pertinax, who was said to have had charismatic imperial presence, approached the invading Praetorian unarmed and tried to overawe them. All but one sheathed their weapons, but that one man's sword was enough to end the 87-day reign of Pertinax.

In the aftermath, there was the "disgraceful" and "unworthy" spectacle of Sulpicianus, who was the father-in-law of Pertinax, and Didius Julianus, a rich parvenu openly bidding against each other for the emperor's purple mantle in the Praetorian camp. Didius Julianus was willing to spend more, so he was proclaimed by the Praetorians and, with their help, intimidated the Senate. The Senate agreed to name him emperor, but the general populace did not go along, and there was serious unrest in the city. Heavenly portents were reported, and there were uprisings further afield. Three separate generals in the provinces each demanded to be Emperor. Septimius Severus, commanding the legions in Panonia, was the eventual winner after outwitting Albinus in Britain, scaring away Niger in Syria, and, of course, and getting the Praetorians to switch sides and abandon Didius Julianus. The Senate promptly condemned Didius to death and named Severus Emperor. Didius Julianus was Emperor for 66 days.

Internet links:

A fascinating contemporary account by historian Cassius Dio (who was in the Senate at the time) is at: http://www.ukans.edu/history/index/europe/ancient_rome/E/Roman/Texts/Cassius_Dio/74*.html. Dio condemns Commodus, paints a flattering portrait of Pertinax, and has not much good to say about anyone else including himself and the other Senators. It was Dio who called the auction at the Praetorian barracks disgraceful and unworthy, but only, perhaps, because it was done openly rather than, as usual, behind closed doors.

Gibbon's "Decline and Fall" account of these events is at: http://www.clas.ufl.edu/users/pcraddoc/dfgib/fourth.htm. The florid language assures that it is not an easy read.

A short modern account of the turmoil of the times is at: http://www.san.beck.org/AB9-RomanTurmoil180-285.html, and a short modern bio of Pertinax is at: http://www.roman-emperors.org/pertinax.htm
 
 

P.S.: Garum was the heavily spiced, salty, and oily fermented fish sauce that the Romans ate with almost everything -- if you wanted to use something similar to make a Roman meal today, you would use Viet Namese nuoc mam or some other South-East Asian fish sauce. Go to http://www.soupsong.com/ffish.html and scroll down to "Fish·As a Flavoring." It is not certain that the Romans originated the expression "a different kettle of fish" but they did say "a different pot of garum."
 
 

Oh, yes, about that "Elvis" in the title: Pertinax, of course, was just his nickname.  His real name was Publius Helvius.  Helvius, in Italian is Elvizio, which, naturally, came into English as Elvis.  Caesar's Palace was never the same without him.