The Praetorians, apprehensive that, in this private contract, they should not obtain a just price for so valuable a commodity, ran out upon the ramparts; and, with a loud voice, proclaimed that the Roman world was to be disposed of to the best bidder by public auction.
This infamous offer, the most insolent excess of military licence, diffused an universal grief, shame, and indignation throughout the city. It reached at length the ears of Didius Julianus, a wealthy senator, who, regardless of the public calamities, was indulging himself in the luxury of the table. His wife and his daughter, his freedmen and his parasites, easily convinced him that he deserved the throne, and earnestly conjured him to embrace so fortunate an opportunity. The vain old man (A.D. 193, March 28th) hastened to the Praetorian camp, where Sulpicianus was still in treaty with the guards; and began to bid against him from the foot of the rampart. The unworthy negotiation was transacted by faithful emissaries, who passed alternately from one candidate to the other, and acquainted each of them with the offers of his rival. Sulpicianus had already promised a donative of five thousand drachms (above one hundred and sixty pounds) to each soldier; when Julian, eager for the prize, rose at once to the sum of six thousand two hundred and fifty drachms, or upwards of two hundred pounds sterling. The gates of the camp were instantly thrown open to the purchaser; he was declared emperor, and received an oath of allegiance from the soldiers, who retained humanity enough to stipulate that he should pardon and forget the competition of Sulpicianus.
It was now incumbent on the Praetorians to fulfil the conditions of the sale. They placed their new sovereign, whom they served and despised, in the centre of their ranks, surrounded him on every side with their shields, and conducted him in close order of battle through the deserted streets of the city. The senate was commanded to assemble, and those who had been the distinguished friends of Pertinax, or the personal enemies of Julian, found it necessary to affect a more than common share of satisfaction at this happy revolution. After Julian had filled the senate-house with armed soldiers, he expatiated on the freedom of his election, his own eminent virtues, and his full assurance of the affections of the senate. The obsequious assembly congratulated their own and the public felicity; engaged their allegiance, and conferred on him all the several branches of the Imperial power. From the senate Julian was conducted, by the same military procession, to take possession of the palace. The first objects that struck his eyes were the abandoned trunk of Pertinax and the frugal entertainment prepared for his supper. The one he viewed with indifference; the other with contempt. A magnificent feast was prepared by his order, and he amused himself till a very late hour with dice, and the performances of Pylades, a celebrated dancer. Yet it was observed, that after the crowd of flatterers dispersed, and left him to darkness, solitude, and terrible reflection, he passed a sleepless night; revolving most probably in his mind his own rash folly, the fate of his virtuous predecessor, and the doubtful and dangerous tenure of an empire, which had not been acquired by merit, but purchased by money.
[The above has been a direct quote from, The Decline and Fall of the Roman Empire by Edward Gibbon, Chapter 5]