COMMODUS.--Rome had enjoyed good government for eighty-four years. This was owing to the fact that her sovereigns had been nominated to their office, instead of inheriting it. None of the emperors during this interval had male children. _Marcus Aurelius_ made the mistake of associating with him in power his son _Commodus_, who was eighteen years old when his father died, and reigned alone from 180 to 192. He began his despicable career as sole ruler by buying peace of the _Marcomanni_ and the _Quadi_. He turned out to be a detestable tyrant, who was likewise guilty of the worst personal vices. He was strangled in his bedroom by one of his concubines, _Marcia_, with the assistance of others, all of whom he was intending to kill. At this time the army, where there had been more energy and virtue than in any other class, began to decline in discipline. Society was growing more and more corrupt. It proves the inherent strength of the organization of the Roman Empire, that, amid all the causes of disintegration and decay, it lasted for two centuries longer. I. EMPERORS MADE BY THE SOLDIERS. We now enter upon a period of military license. The emperors are appointed by the soldiers. The rulers, when the soldiers fall out with them, are slain. In the course of ninety-two years, from 192 to 284, twenty-five emperors, with an average reign of less than four years for each, sat on the throne. Only two reigns exceeded ten years. Ten emperors perished by violence at the hands of the soldiers. A real advantage in this way of making emperors, was, that supreme power might thus devolve on able generals; but another, and a fatal result, was the demoralizing of the armies, by whose favor the rulers of the state were set up and pulled down. TO ALEXANDER SEVERUS (A.D. 222).--The assassins of Commodus, with the assent of the praetorians, made a worthy senator, _Pertinax_, emperor; but his honesty and frugality, and his disposition to maintain discipline among the soldiers, caused them to murder him three months after his accession (193). It is said that they then sold the imperial office at auction to a rich senator, but the leaders of the armies in different regions refused their consent. Of these, _Septimius Severus_ (193-211) made his way to the throne, and put down his rivals. The empire became a military despotism. A garrison of forty thousand troops, the prefect of whom was in power second only to the sovereign, took the place of the old prætorians. _Severus_ was a good general. In a war against the Parthians, he captured Ctesiphon, their capital. _Caracalla_, his son (211-217), was a base tyrant. He was murdered by the prætorian prefect, _Macrinus_, who reigned for a short time (217-218), but perished in consequence of his attempts to reform the discipline of the army. _Heliogabalus_ (218-222) was not more cruel than others had been, but his gross and shameless debauchery was without a precedent.