Marcus Didius Severus Julianus was the son of Quintus Petronius Didius Severus, member of one of the most important families of Mediolanum (Milan).
Pertinax' death left Rome without any successor. More so the real decision over who was to be emperor lay undoubtedly with the praetorians, who had just disposed of the last one.
What now ensued was a farce, the likes of which the Roman empire had never seen. Sulpicianus and Didius Julianus, began to outbid each other, Sulpicianus inside the camp, Julianus outside, passing his figure on to messengers who carried the figures back and forth.
As the bids went up and up, Sulpicianus finally reached the sum of 20'000 seserces for each praetorian. At this moment Julianus decided not to continue bidding a little more every time, but simply announced aloud that he'd pay 25'000 seserces per head. Sulpicianus did not raise.
The soldiers had two reasons to decide for Julianus. Their first and most obvious one was that he offered them more money. The other was that, and Julianus didn't fail to mention this to them, Sulpicianus might well seek to avenge his son-in-law's murder when he came to the throne.
As crass as this auction no doubt was, it has to be seen in the context of successive Roman emperors who had paid out large bonuses upon taking office. When Marcus Aurelius and Lucius Verus acceded to the throne they paid the praetorians 20'000 sesterces a soldier.
The senate was naturally not too pleased at the way by which the office had been secured. (After all, at the death of Domitian it had been the senate who chose Nerva for the vacant throne, not the praetorians!). But opposition by the senators was impossible. Julianus arrived at the senate with a contingent of praetorians to enforce his will. So, knowing that opposition would mean their death, the senators confirmed the praetorians' choice.
Julianus' wife Manlia Scantilla and daughter Didia Clara were both granted the status of Augusta.
Laetus, the praetorian prefect who had been the chief conspirator in the murder of Commodus was put to death by Julianus, who announced he sought to honour the memory of Commodus (most likely to justify his succession of the murdered Pertinax).
Julianus made many promises to the population of Rome, trying to win their support, but the public dislike of the man who had bought the throne only increased. There was even demonstrations in the street against Julianus.
But now other, far more powerful threats to Julianus than the civilian people of Rome began to arise. Within a very short time Pescennius Niger (governor of Syria), Clodius Albinus (governor of Britain), and Septimius Severus (governor of Upper Pannonia) were declared emperors by their troops.
Severus moved fastest, gained the support of the entire Rhine and Danube garrison (16 legions !) and came to agreement with Albinus, offering him the title 'Caesar' to buy his support.
Julianus tried his all to fortify Rome, as it had no defences at that time. But the praetorians were no friends of hard labours such as digging ramparts and building walls and they did everything to avoid them. But then the praetorians had lost much of their faith in Julianus when he had failed to pay them their promised 25'000 sesterces a head. Now, in this time of desparate crisis, he quickly made payment of 30'000 seserces per man, but the soldiers were well aware of his reasons. Marines were brought in from Misenum, but they turned out to be a rather undisciplined rabble and hence were pretty useless.
Assassins were sent forth to murder Severus, but he was too closely guarded.
Desparate to save his skin, Julianus now sent a senatorial delegation to Severus' troops, trying to use the respect for the ancient senate to order the soldiers to return to their bases in the north.
In a strange desparate bid, Julianus now even tried to switch sides, asking of the praetorians that they should hand over the murderers of Pertinax and should not resist Severus' troops on arrival. The consul Silius Messalla learnt of this order and decided to call a meeting of the senate. It might well have been that the seante was being sidelined - and a possible scapegoat - by this political manoeuvre of Julianus. For on 1 June AD 193, with Severus only days away from Rome, the senate passed a motion sentencing Julianus to death.
All was lost and Julianus knew it. He withdrew into the palace together with his son-in-law Repentius and the remaining praetorian comander Titus Flavius Genialis.