Historians of the Roman Empire refer to the period following the death of Alexander Severus in 235 AD to the accession of Diocletian to the imperial throne in 284 AD as the “Crisis of the Third Century.” There were five reasons for this crisis:
- Invasions from Germanic barbarians east of the Rhine and north of the Danube and from Sassanid Persians to the Roman Empire’s easternmost border.
- The so-called “barracks emperors”—commoners, often from the outskirts of the Roman Empire, who had ascended the ranks of the military and garnered (temporarily) support from the troops—died in battle or were killed by the disenchanted troops who had put them in office. There were twenty-six emperors in this fifty year period.
- As a result of civil war, the Roman Empire was divided into three competing empires—the Western Gallic, the Central Roman, and the Eastern Palmyrene.
- Given that there had been no expansion since the reign of Hadrian (117-138 AD), the Roman Empire had lost a significant source of its income: conquest. This was compounded by the economic problems of barracks emperors being forced to pay the military to stay in power, paying off barbarian invaders, the expenses of the bread and circuses, inflation as a result of devaluing the denarius, and a decrease in trade.
- Plague struck in 250 AD, killing, it was said, 5,000 a day in Rome.