Herodian (late second, first half third century): Greek historian, author of a History of the Roman Empire since the Death of Marcus Aurelius in which he describes the reign of Commodus (180-192), the Year of the Five Emperors (193), the age of the Severan dynasty (211-235), and the Year of the Six Emperors (238).
The translation was made by Edward C. Echols (Herodian of Antioch's History of the Roman Empire, 1961 Berkeley and Los Angeles) and was put online for the first time by Roger Pearse (Tertullian.Org). The version offered on these pages is hyperlinked and contains notes by Jona Lendering.
Conspiracy of Perennis
[1.9.1]  After he had removed the men whom Commodus had reason to fear, those who showed him good will for his father's sake, and those who were concerned for the emperor's safety, Perennis, now a powerful figure, began to plot for the empire. Commodus was persuaded to put the prefect's sons in command of the army of Illyricum, though they were still young men; the prefect himself amassed a huge sum of money for lavish gifts in order to incite the army to revolt. His sons quietly increased their forces, so that they might seize the empire after Perennis had disposed of Commodus.
[1.9.2] This plot came to light in a curious fashion. The Romans celebrate a sacred festival in honor of Jupiter Capitolinus, and all the stage shows and athletic exhibitions are sent to take part in this festival in the capital. The emperor is both spectator and judge, together with the rest of the priests, who are summoned in rotation for this duty.
[1.9.3] Upon his arrival for the performance of the famous actors, Commodus took his seat in the imperial chair; an orderly crowd filled the theater, quietly occupying the assigned seats. Before any action took place on the stage, however, a man dressed as a philosopher (half-naked, carrying a staff in his hand and a leather bag on his shoulder) ran out and took his stand in the center of the stage. Silencing the audience with a sweep of his hand, he said:
[1.9.4] "Commodus, this is no time to celebrate festivals and devote yourself to shows and entertainments. The sword of Perennis is at your throat. Unless you guard yourself from a danger not threatening but already upon you, you shall not escape death. Perennis himself is raising money and an army to oppose you, and his sons are winning over the army of Illyricum. Unless you act first, you shall die."
[1.9.5] Whether he said this by divine inspiration, or whether, obscure and unknown before, he was making an effort to gain fame, or hoped to receive a generous reward from the emperor - whatever the reason, Commodus was thunderstruck. Everyone was suspicious of the man's words, and no one believed him. Perennis ordered the philosopher to be seized and burned for making insane and lying accusations.
[1.9.6] Such was the penalty that the beggar paid for his ill-timed outspokenness. The emperor's intimate friends, however, who had long been secretly hostile to Perennis (for the prefect was harsh and unbearable in his insolence and arrogance), believed that the time had come and began to bring charges against him. As a result, Commodus escaped the plot, and Perennis and his sons perished miserably.
[1.9.7] For not much later, some soldiers visited Perennis' son in secret and carried off coins bearing the prefect's portrait. And, without the knowledge of Perennis, the praetorian prefect, they took the coins directly to Commodus and revealed to him the secret details of the plot. They were richly rewarded for their service.
[1.9.8] While Perennis was still ignorant of these developments and anticipated nothing of the sort, the emperor sent for him at night and had him beheaded. And he dispatched men to Perennis' son by the fastest route, so that they might reach him before he knew what had happened. These men were to take a route shorter than the one by which news was regularly carried; in this way they would be able to come to the youth before he was aware of events at Rome. Commodus wrote the youth a friendly letter, telling him that he was recalling him to greater expectations, and ordering him to come to Rome.
[1.9.9] Perennis' son knew nothing of the reception awaiting him and was unaware of his father's fate. When the messengers informed him that his father had given these same orders orally but, satisfied with the emperor's letter, had not written a separate note, the youth was convinced, although he was concerned about leaving the plot unfinished. Nevertheless, relying on his father's power as if that power still existed, he left Illyricum.
[1.9.10] On the way to Italy the youth was killed by the emperor's men. Such was the fate of Perennis and his son. Thereafter Commodus regularly appointed two praetorian prefects, believing that it was safer not to place too much authority in the hands of one man; he hoped that this division of authority would discourage any desire to seize the imperial power.