I think this is something many folks suspected …

Military warmongers took over the Roman Empire in the third century. The senate, the administrative elite of the Roman empire watched from the sidelines. Dutch researcher Inge Mennen investigated the balance of power in Imperium Romanum during the ‘crisis of the third century‘. Conclusion: senators lost their military power but retained their status. Meanwhile military emperors pulled the strings.

Inge Mennen studied biographies of the most prominent men from the turbulent third century to gain an impression of the shifts in the balance of power.

For decades power in ancient Rome was in the hands of the senators who traditionally came from a small group of wealthy aristocratic families. Status and network paved the way to the top. Military experience assumed second place. The senate was also the rearing ground for future emperors: only the ordo senatorius could cultivate emperors. At least that was the case until the third century AD. Then senators had to make room for men of an utterly different class: military emperors from the equestrians. Within just 100 years the Roman Empire changed almost beyond recognition: emperor Diocletianus realised large-scale reforms. He reorganised the army and shared the power with his most important general. The Roman Empire was then effectively split in two. How could that have happened within such a relatively short space of time? Inge Mennen attempted to answer this question.

Elite

In the third century the border areas of the immeasurably large empire came under pressure. Emperors had to spend increasing amounts of time dealing with the far corners of the empire and the increasing threat of war. Senators, with their limited military experience, were overshadowed by military leaders. Yet Inge Mennen’s research also reveals that some of the senators managed to use the new situation to their advantage. They retained their high social position but at the same time quietly expanded their power in the more peaceful parts of the empire. They relinquished some of their military might but flourished in legal, administrative and financial positions. Appointments up to the level of the senate were made via the emperor who in this way honoured the elite of Rome and at the same time could consolidate his own power.
Equestrians

Meanwhile the ‘new era’ at the start of the tumultuous crisis century ensured the expulsion of the equestrians from Rome. For a long time equestrians had occupied mainly advisory positions in the emperor’s palace. Yet with the absence of the emperor in times of war and the increasing power of cunning senators, this group became superfluous. That left the equestrians with just one option: defending the empire. Professional soldiers also saw an opportunity to climb up to the equestrians via a career in the army. Gradually the composition and culture of this social class changed. The Roman Empire at war made grateful use of this growing group of warmongers: they now advised the emperor and controlled the border areas. Equestrians who had won their spurs in the Roman army even rose to the rank of emperor, an honour which up until that time had been the exclusive privilege of the senators.
Emperors

The senators continued to control Rome, the empire’s old seat of power, whereas the equestrians gained increasing control of the periphery of the empire. The focus came to lie on the peripheral provinces, in the regions of the empire where wars had to be fought. In order to retain control of these areas the emperors needed a military background. They also devoted an increasing proportion of their time to military matters and so they frequently felt obliged to put off other tasks. At the worst of times, the emperors were even forced to give up parts of their empire.

The old imperial dynasties were not reinstated in the third century. Instead military emperors emerged: powerful generals who, with the support of their troops, gained the emperorship for a short period of time. They reigned until the next coup by an ambitious general. Military and civil affairs came into the hands of two completely different groups until these issues were formally separated by emperor Diocletianus. According to Inge Mennen, the reforms implemented by this emperor are not as radical as they might initially appear. The biographies of the powerful men of the third century reveal that many changes had already been set in motion a good century previously. Although Diocletianus put these ideas in writing, they were not entirely new.

via Warmongers pushed ‘intellectual’ politicians aside | AlphaGalileo.