According to Cassius Dio, Marcus Didius Severus Julianus was born in Milan on January 30, 133 AD to Quintus Petronius Didius Severus and Aemilia Clara. His father hailed from a prominent Milanese family and his North African mother from a family of rank of consuls. This well-connected parentage afforded him the opportunity to be raised in the house of Domitia Lucilla, the mother of emperor Marcus Aurelius.
Domitia helped Julianus attain his first appointment at an early age – a member of the vigintivirate, a college of twenty minor magistrates in charge of everything from lawsuits to road maintenance to casting and striking coins. This college was often a stepping-stone of the sons of senators to begin their public careers and even Julius Caesar served in it as curator viarum. While in office, he married Manlia Scantilla and around 153 they had a daughter, Didia Clara.
Julianus continued on his successful career, being promoted through the positions of quaestor, and aedile, finally becoming praetor around 162. He next took command of Legio XXII Primagenia in Mogontiacum (modern-day Mainz, Germany) and in 170, became the praefectus of Gallia Belgica (modern-day parts of France, Belgium, Luxembourg and the Netherlands). He remained praefectus for five years, until being raised to co-consul with Pertinax, through his handling of an uprising of the Germanic Chauci. Next, he campaigned against the Chatti and went on to rule Dalmatia and Germania Inferior.
During his next assignment, as prefect in charge of distributing money to the poor in Italy, he was charged with conspiracy by then emperor, Commodus. He was acquitted and went on to govern Bithynia and then succeeded Pertinax as proconsul of Africa.
Pertinax was hailed emperor after the assassination of Commodus on December 31, 192, and ruled for 86 days, until he was assassinated by the praetorian guards. The Roman Empire was then without a clear successor, so Flavius Sulpicianus, father-in-law of Pertinax, appealed to the praetorian guard while in their camp to hail him as emperor, by making offers. While this was going on, Didius Julianus got wind of what was happening and quickly went to the camp to make his own offers. Essentially, Sulpicianus and Julianus bid back and forth until Sulpicianus offered 20,000 sestertii per guard. Julianus, one of the wealthiest men in Rome, thanks to his long and successful career and his family lineage, countered with 25,000 sestertii – an amount no one else could touch. The guards accepted the offer and marched the new Caesar to the Senate, who was forced to accept him, and his wife and daughter were both named Augustae.
Although the Senate had no choice to name Julianus emperor, the people didn’t like the fact the praetorians just sold the Empire to the highest bidder after murdering the previous emperor. Pleas were sent to the leaders of the frontiers to come to Rome and deal with the situation and three generals responded – Clodius Albinus in Britain and Hispania; Pescennius Niger in Syria; and Septimius Severus in nearby Pannonia.
In order to pay for the obscene offer he made to the guards, the first thing Julianus did was devalue the currency and change the purity of the silver coinage from 87% to 81.5%. He also realized he was going to have a problem with the people and the armies, so he commanded the praetorian guard to begin training for any upcoming confrontations, as they had not seen active duty for a long time.
Septimius Severus, being the closest in proximity to Rome, had the advantage. He rallied his three legions, promised them a generous bonus, promised the rank of Caesar to Clodius Albinus, and quickly advanced on the capitol. Julianus declared Severus an enemy of the state, sent assassins to deal with him and tried to change the loyalty of the troops, all to no avail. Severus easily defeated the guards he encountered and to avoid as much bloodshed as possible, promised the rest of the guards he would spare them if they would turn over the ones responsible for murdering Pertinax. Seeing the writing on the wall, and still not having received the bribe of 25,000 sestertii promised by Julianus, the guards accepted the terms and told the Senate of their intentions. The Senate, relieved with the developments, deified Pertinax and declared Septimius Severus emperor.
The praetorians turned over the conspirators as Severus requested and Julianus was captured and beheaded, a mere 66 days into his reign.