The reign of Marcus Didius Severus Julianus is largely insignificant and unremarkable except for the nature in which it began, and its direct influence on the outbreak of civil war. It was Didius Julianus who bought the throne from the very same praetorians who assassinated Pertinax, his imperial predecessor.
Didius Julianus was born January 29, AD 137 likely in Mediolanum (Milan) into a prominent political family of the era. He was raised in the house of Domitia Lucilla (the mother of Marcus Aurelius) and enjoyed her support, as well as her son’s, throughout his early career. As such, Didius Julianus rose steadily through the ranks of the cursus honorum reaching the post of quaestor a year before the ‘legal’ age (such legalities were often overlooked for the immediate court of the imperial family). After a term as aedile and as praetor, Marcus Aurelius appointed him to the command of Legio XXII Primigenia in Germania, and then served as governor of Belgica where he defended the province from incursions of the Germanic Chauci. This command earned him the consulship and he went on to govern with distinction in Dalmatia and Germania Superior and to serve as praefectus alimentorum in Italy (responsible for grants of money and welfare to the poor).
During the reign of Commodus, Didius Julianus was briefly suspected of involvement in a plot against the emperor’s life, but this suspicion seems to have been short lived. He quickly returned to the emperor’s favor and the governorship of Bithynia. After Bithynia, his career seems to have mirrored that of future emperor Pertinax. Julianus served as a suffect consul with Pertinax and followed him as governor of Africa prompting Pertinax to prophetically refer to him as “my colleague and successor.”
Shortly thereafter, Commodus was assassinated and Pertinax appointed to replace him (December 31, AD 192/January 1, AD 193). The reign of Pertinax was in turn undermined by the praetorians and he met a violent death at their hands in just 3 months (March 28, AD 193). The events that followed left a lasting stigma on the effectiveness of Roman succession policy and the praetorian guard as a political force. City prefect Flavius Sulpicianus (Pertinax’ father-in-law) approached the praetorian camp in an attempt to gain the empire for himself but seems to have been met with resistance from the praetorians. Perhaps fearing retribution from a relative of the murdered Pertinax for their part in his death, some of the men entered the city looking for alternative candidates. While most viable candidates likely locked themselves in their homes to wait out the crisis, they did find the opportunistic Didius Julianus and brought him to the camp.
With Sulpicianus on the inside and Didius Julianus without the two men began to make offers to the soldiers for their support. Monetary offers were waged against one another until ultimately Didius Julianus purchased the throne for 25,000 sesterces per Praetorian, according to contemporary historian and senator Dio Cassius. (With 10 double strength praetorian cohorts of approx. 800 men, the total payment may have been as much as 200 million sesterces or 50 million denarii). The Historia Augusta suggests that Didius Julianus actually ended up paying some 30,000 sesterces but another contemporary (Herodian… though a child at the time) disputes this entirely, suggesting that the funds simply weren’t available to make good on the promised payments. Additionally, Didius Julianus promised to restore the name of Commodus (which had been stricken from various public monuments and records) who had been very popular with the army. Sulpicianus’ connection to Pertinax on the other hand, and therefore the faction that ultimately replaced Commodus, likely did little to endear him the praetorians (though he did emerge from his imperial bid completely unharmed).
The senate did confirm Julianus as a legitimate successor to Pertinax preserving his place in the official list of “emperors”, but his reign was effectively little more than a passing moment in time. Despite his prominent political career, he seems to have had little support from the rest of the aristocracy. Dio Cassius’ account is particularly unflattering and he describes the populace as openly hostile. Whether the citizens were angry over the murder of Pertinax, the preceding assassination of Commodus or the unseemly sale of the empire to Julianus, or a combination thereof is debatable. However, it can be reasonably assumed that revolt among the people had a direct impact on the outbreak of legionary revolt and eventual civil war. While the legions were likely still hostile regarding the treatment of their favored Commodus, open protest by the people may have inspired the rebellion of Pescennius Niger, the governor of Syria. Whether Niger had already been declared emperor by the legions immediately after the death of Pertinax is not entirely clear, but he does seem to have been inspired by calls from the citizens of Rome to come to their aid.
Despite the revolt of Niger and the Syrian legions, Julianus still had little concern for the continuation own authority. It was not until Niger was followed shortly after by Clodius Albinus in Britain and Septimius Severus in nearby Pannonia that Julianus grew understandably distressed. Agents sent against Severus, who had begun a march to Rome, were either defeated or defected to Severus’ side and there was little to stop his impending approach. Julianus attempted to negotiate a co-emperorship with Severus and even executed Laetus and Marcia (Commodus’ praetorian prefect and his concubine respectively who were deeply responsible in the assassination) in an attempt to appease the legions, but there was little hope of stopping Severus who found no resistance in his march. The praetorians understood their own precarious predicament and once again took matters into their own hands.
Assured by Severus that they would be left unharmed if they arrested the murderers of Pertinax and kept the peace in the city (essentially taking orders from Severus and isolating Julianus), the praetorians effectively switched sides. Dio Cassius describes the end of Julianus’ reign thusly:
“We (the Senate) thereupon sentenced Julianus to death, named Severus emperor, and bestowed divine honors on Pertinax. And so it came about that Julianus was slain as he was reclining in the palace itself; his only words were, "But what evil have I done? Whom have I killed?" He had lived sixty years, four months, and the same number of days, out of which he had reigned sixty-six days.”