I knew this would create some interesting discussion. There were three great plagues that hit the empire between 165AD and 275AD which lasted for a totlal of 40 years or more. Your point about the 3 Parthicae legions raised by Septimus is interesting and Ibeji does rasie this. To quote "On the face of it, such massive recruitment would seem to contradict the picture of manpower problems hinted earlier." Ibeji goes on to say that other historians (Mommsen) believed that Legio I Parthica was raised prior to Septimus, "basing his assumptions on the inscription of C. Iulius Pacatianus, the first commander of the legion" (p. 77), so he would have only raised the other two. Again Ibeji says that just before the time of raising the Partica legiones Septimus greatly increased the condtions of service including pay and would have assisted in gaining additional recruits. Such measures were necessary as by the end of the second century the army was finding it difficult to recruit men, which were exacerbated by out of date rates of pay, restrictive terms of service and prohibitive length of enlistment (Ibeji, p. 81). The 3 legions that Septimus raised were at the beginning of the third century prior to 50 years on continual warfare, pestilence, famine and natural catastrophies.