By the later third century an emperor generally needed to be successful in war to survive. It is true to say that emperors were compelled to think more and more about their personal security against revolt, preparation for warfare and the waging of war. Maximinus, who overthrew the last member of the Severan dynasty, Severus Alexander, emphasized in his propaganda campaign that Alexander was a mummy’s boy, militarily incompetent and parsimonious - in contrast to Maximinus, who was a real soldier’s man.59 The fact that Alexander was involved in long wars made these jibes more effective. However, as emperors became more associated with military life it became more difficult to distance them from military failure, and setbacks were directly laid at their door. We may remember by contrast how Augustus had skilfully isolated himself from the destruction of three legions in Germany, which was blamed on the incompetence of the luckless commander, Varus.60 Indeed, an emperor’s military ability became more important as foreign wars became more frequent and dangerous, and the empire faced serious foreign invasions. If men felt that they needed someone of imperial rank on hand to command the troops, repel incursions and keep the empire together, then that would lead to frequent usurpations as ambitious contenders promised to rescue the empire by their military prowess and tried to persuade senior officers and the soldiers. This in turn could lead to an increased role for the army in politics, as soldiers supported various candidates for the purple, and also to fragmentation of the imperial structure as strong leaders emerged who based their rule on their ability to protect a single territorial area, like Postumus and his Gallic empire, and later Odenathus in Palmyra.61 Diocletian recognized these developments when he reorganized the empire in the late third century by creating a structure in which two emperors (Augusti) ruled jointly, supported by two junior partners (Caesars). In practice, this system, known as the Tetrarchy, meant that each of the four rulers took responsibility for a part of the empire, increasing military efficiency and personal security through the speed of reaction to invasion or revolts. This was perhaps the only way in which central control could be re-established. Eventually, in the fourth century as the government became desperate for good soldiers, warlords in command of private armies offered their services and supported Rome’s interests as suited their personal inclinations.
It is doubtful, however, if soldiers had any more say in political life than before. They were essentially the pawns of groups of officers or other important men who bribed or cajoled them to support certain candidates. In constitutional terms the senate, and through it the people, were still the legitimating bodies, however much in reality the leading generals dictated the choice of emperor. In the dissemination of information and the promotion of their image, emperors still maintained the traditional slogans about imperial qualities and the government of the Roman state. Policy was not formulated in the interests of soldiers or any specifically military ideology.
Andreski thought that praetorianism became particularly acute in Rome ‘when promotion from the ranks to the highest posts became common’.62
From the mid-third century there was certainly greater social mobility, in that men of equestrian rank were now being appointed to more senior posts previously held by senators, such as the command of a legion. These men usually had more military training and experience than senators, and it will have made less sense to appoint a senator with limited military experience as governor of a province where he was in command of several legions and auxilia. Gradually equestrians began to be appointed to more senior posts, often with the title dux, in command of substantial bodies of troops. Senators were phased out of provincial governorships involving the command of legionary troops, and ad 260 saw the last known example of a senator in command of a military campaign. Equestrians employed in this way tended to be schooled in military affairs and were often promoted from highly experienced centurions and senior centurions. Thus the way was opened for people from different regions and social backgrounds to assume a greater role in Roman society and government, as the empire moved further away from its Italian homeland and the army became steadily less Roman in character. Many of these tough military officers came from the Danubian provinces, and the marriage of military ability and imperial responsibilities eventually brought emperors of Illyrian stock like Diocletian and Constantine. Yet Augustus would still have recognized the political and military framework, and when Constantine died in 337 he had secured the unity and prestige of the empire while remaining the master of his army and preparing for an orderly, hereditary succession.
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