I saw on wiki that the Pax Romana is considered to have ended in 180 CE. That's a bit odd, IMO, and contrary to what an old history text said. The end of the period of the Good emperors shouldn't be confused with the end of the pax Romana. Ironically, the reign of Commodus, after 180, was far more stable than that of Marcus Aurelius. I incline toward the view, expressed in a former schoolbook, that the pax Romana ended with the death of Alexander Severus, inasmuch as civil wars and internal insecurity were the exceptions prior to 235-284, and commonplace during that period, and subsequently.