Barracks emperor in the context of "Aureus"

The antoninianus or pre-reform radiate was a coin used during the Roman Empire thought to have been valued at 2 denarii. It was initially silver, but was slowly debased to bronze with a minimal silver content. The coin was introduced by Caracalla in early 215 AD. It was silver, similar to the denarius, except that it was slightly larger and featured the emperor wearing a radiate crown, indicating it was a double denomination. Antoniniani depicting women (usually the emperor's wife) featured the bust resting upon a crescent moon.

Even at its introduction, the silver content of the antoninianus was only equal to 1.5 denarii. This created inflation: people rapidly hoarded the denarii (Gresham's law), while both buyers and sellers recognized the new coin had a lower intrinsic value and elevated their prices to compensate. Silver bullion supplies began running short because the Roman Empire was no longer conquering new territory, the Iberian silver mines had been exhausted, and a series of soldier emperors and usurpers needed coin to pay their troops and buy their loyalty. Each new issue of the antoninianus thus had less silver in it than the last, and thus contributed to ever-increasing inflation.

The Illyrian emperors (Latin: Illyriciani) were a group of Roman emperors during the Crisis of the Third Century who were of Illyrian origin and hailed from the region of Illyria (Latin: Illyricum, in the Western Balkans), and were raised chiefly from the ranks of the Roman army (whence they are ranked among the so-called "barracks emperors"). In the empire the Illyrian generals had established a powerful military caste.

In the 2nd and 3rd centuries, the Illyricum, which included the provinces on the Lower Danube (Dacia, Raetia, Pannonia, Moesia), held the largest concentration of Roman forces (12 legions, up to a third of the total army), and were a major recruiting ground. The advance of these low-born provincials was facilitated by a major shift in imperial policy from the time of Gallienus (253–268) on, when higher military appointments ceased to be exclusively filled by senators. Instead, professional soldiers of humble origin who had risen through the ranks to the post of primus pilus (which also entailed admission to the equestrian order) were placed as heads of the legions and filled the army's command structure.