Casperius Aelianus (c.45-98): praetorian prefect of the Roman emperors Domitian and Nerva.
His early career is poorly understood, but Philostratus, a Greek author writing in the first half of the third century, records that Aelianus was a military tribune in the army of Vespasian, who had been sent by the emperor Nero to Judaea to suppress the Jewish revolt. During this war, Nero's reign came to an end (in 68) and a civil war broke out, in which Galba, Otho, and Vitellius. Vespasian also tried to become master of the Mediterranean Empire (the "year of the four emperors", 69). Vespasian, who occupied Alexandriaand cut off Rome's Egyptian food supply, was ultimately victorious and was to reign the Mediterranean world until 79. According to Philostratus, Aelianus was in Vespasian's army and visited Alexandria. Although Philostratus' Life of Apollonius is not the most reliable of all ancient sources, there is no evidence to contradict this statement.
Aelianus' further career is unknown, but it is certain that during the reign of Vespasian's son Domitian (81-96), he was one of the two praetorian prefects, which meant that he commanded the imperial guard in Rome. He was responsible for the safety of the emperor and may have taken part in his Germanic or Dacian wars. It was not uncommon that the officers who occupied this position had first been governor of Egypt, and this may have been a step in Aelianus' career as well, although there is no evidence to prove this.
If we are to believe Philostratus, Aelianus used his position as praetorian prefect to protect the Cappadocian philosopher Apollonius of Tyana when he had to defend himself against several false charges. Again, there is no evidence that confirms or contradicts Philostratus' statement.
By 94, Aelianus was no longer in command of the guard. There is no need to believe that he had fallen out of favor. If he had been a tribune in 69, he was born in c.45 and must have been almost fifty when he retired. By ancient standards, he was an old man and may have been unsuited to be a fighting officer. On the other hand, the reign of Domitian was becoming increasingly tyrannical, and many officials preferred to retire to their country estates. Those who stayed, men like Pliny the Younger, rapidly advanced in their careers.
The new prefects of the guard were Titus Petronius Secundus, former governor of Egypt, and a man named Norbanus, former governor of Raetia and a war hero who had saved Domitian's throne when Saturninus, the commander of the Upper Germanic army, had revolted. In 96, when Domitian was assassinated, these two men acquiesced in the situation and made sure that the guard accepted the new emperor, the elderly Nerva. The details of this coup are unclear, but it is certain that both prefects knew what was afoot and did not intervene.
Norbanus may have been assassinated, though; he is not heard of anymore. Nerva was able to dismiss Petronius, but we do not know how and when. Because he had gained his throne by a coup d'état, he needed a strong supporter, and he asked Aelianus, who was left without colleague. It is possible that the new emperor had been forced to appoint this man because the soldiers, who he had to keep satisfied, had demanded the return of their former commander. What happened next, in July or August 97, is told by the historian Cassius Dio:
Casperius Aelianus, who had become commander of the praetorians under Nerva as he had been under Domitian, incited the soldiers to mutiny against him, after having induced them to demand certain persons for execution. Nerva resisted them stoutly, even to the point of baring his collar-bone and presenting to them his throat; but he accomplished nothing, and those whom Aelianus wished were put out of the way.note[Cassius Dio, Roman History, 68.3.3; tr. E. Cary.]
There's more than meets the eye. Dio says that Aelianus incited the men, but their demands were not those of outraged soldiers: they only wanted the execution of Domitian's actual assassin and their former commander Petronius, who was held co-responsible. During the crisis of 69, the members of the praetorian guard had been a lot less moderate. This was not a coup or a serious riot - it was a calculated attempt to put pressure on a weak emperor.
It is known that in the winter of 96/97 and the spring of 97, there were great tensions. Powerful governors were considering their chances to become emperor. A man named Crassus attempted a coup. There was a serious disturbance in Syria. And now, the guard had shown its teeth. It is reasonably clear that the restrained action of Aelianus' men was sufficient to convince Nerva that he had to expand his power base by appointing a reliable general as his successor. This happened two or three months later, in October, but Cassius Dio ignores this interval and adds to the lines quoted above:
Nerva, therefore, finding himself held in such contempt by reason of his old age, ascended the Capitol and said in a loud voice: "May good success attend the Roman Senate and people and myself. I hereby adopt Marcus Ulpius Trajan." Afterwards in the Senate he appointed him caesar and sent a message to him written with his own hand (Trajan was governor of Germany).note[Cassius Dio, Roman History, 68.3.3; tr. E. Cary.]
In Dio's view, the revolt of the praetorians was the immediate cause of Nerva's decision. It may have been more complex, but after Aelianus' action, it was impossible that the new emperor would chose a non-military man. The only candidate with sufficient military experience, consular ancestry, and connections was Trajan.
We will never know what happened exactly. After all, conspiracies are usually secret until their members have reached their aims, and they are immediately covered up afterwards. It is possible that Aelianus acted on behalf of Trajan, or wanted to prevent a civilian from becoming emperor. However this may be, his action was sufficient to force Nerva to announce his choice.
In January 98, Nerva died of natural causes. Trajan, who was in Cologne, accepted the empire, and stayed north of the Alps for some time. Cassius Dio says:
He sent for Aelianus and the praetorians who had mutinied against Nerva, pretending that he was going to employ them for some purpose, and then put them out of the way.note[Cassius Dio, Roman History, 68.5.4; tr. E. Cary.]
We do not know what "put them out of the way" means. It may be that the men were killed, but it is also possible that they were requested to retire.