This paper will examine the praetorian prefect’s transition from a military to an administrative role. The prefects started out as simply the commanders of the praetorian guard and among the emperor’s chief generals. However, by late antiquity the prefects were among the most powerful civil officials in the state. As second only to the emperor in judicial, administrative, and land tax matters they were able to exert their authority over all areas in their quarter of the empire. The shift from a predominately military to an entirely civil post is the largest change that the institution underwent during its lifetime.
The shifting duties of the prefect are connected to the third century “crisis” and the changing form of the empire during this era. While many secondary works have noted the change in the prefect’s role, few have attempted to define them and none have made a study of the shift. Laurence Lee Howe’s The Pretorian Prefect from Commodus to Diocletian (Chicago, 1942) probably comes the closest as it identifies some of the key changes, but it ends in 305 which means that it does not engage with the later changes or try to identify their origins. Bennet Salway’s DPhil thesis The Creation of the Roman State, AD 200-340 (Oxford, 1994) has some important insights but its focus is on the later period. For the earlier period, Michel Absil’s Les Préfets du Prétoire d’Auguste à Commóde (Paris, 1997) is very useful but ends just before the period in question.
In this paper, I will argue that the administrative roles of the praetorian prefect were largely acquired during the period of child emperor rule in the beginning of the third century and not as part of Diocletian’s restructuring at the end. The period of child emperor rule required the prefect to assume many of the roles that had previously been the responsibility of the emperor. This included the responsibility for supplying the army, which turned into an overall responsibility for taxation when the annona militaris became the chief land tax of the empire. The core of this argument is a prosopographical study of those third century prefects whose early careers can be reconstructed. The number of prefects from administrative backgrounds show a clear increase under child emperors like Alexander Severus, and the earliest prefects with a documented role in supplying the army come under Gordian III. Rather than their administrative roles becoming stronger in the second half of the third century, there is actually some evidence of emperors resisting them. Under Valerian we can identify a different official controlling army supply and prefects chosen for their military backgrounds. These efforts to return the prefect to its original role failed, and long before the time of Diocletian the prefect was the highest official in both military and administrative spheres. As this paper will show, the third century is the most important period to understand when examining the prefect’s role.