The Roman Army in the Late Roman Empire   

By the end of the third century A.D., the empire was getting plagued by civil war and barbarian invasions.  Eventually the old legions became disorganized and spread out.  Cohorts were disbanded and others were sent to various regions to fill gaps in the defense.  Legions were spread out across the empire’s now huge territory.  The empire had now expanded and subjugated many territories and people, and with that came the recruitment of non-Romans into the army.  It helped appease and control the newly won areas by offering citizenship at the end of a military career.

The practice of allowing non-citizens to join the army began after the Marius Reforms.  “The link between citizenship and military service” was now severed.  Especially during the civil war period when many legions were raised, men were recruited to the army even though they lacked the essential requirement:  citizenship.  Especially when the Empire became so large that it was divided into the East and West Empires, “the imperial authorities found it difficult to recruit citizens over large areas of the empire”.  This meant that when a barbarian or other enemy threat arose in different areas of the east and west empire, it was easier to raise barbarian armies and use ally troops as a large chunk of the army, instead of having a “one size fits all” professional army across the whole empire.  It was not that the Roman Empire’s citizen population was declining during this period.  On the contrary, citizenship had never been higher, and there could have been a steady flow of Roman citizens into the army if the imperial authorities did not rely so much on mercenaries and barbarians. This in the end, as we will see, directly contributed to the fall of the Roman Empire.

From the start of the empire to the end, the army steadily became more culturally diversified.  By the third and fourth century, the army increasingly relied on employed barbarians and allies to do the fighting, instead of training the vast population of Roman citizens.  The army became more of a “mercenary” body, as the number of allied troops outnumbered the Roman ones.  This diluted the once proud and powerful army into a mixture of unreliable troops.  By the fifth century, the Roman army of the western empire had all but disappeared, and soon after that, the Roman Empire fell.  In this way, the choice to create an army that included newly conquered enemies and untrustworthy allies destabilized the balance of power within the army, which eventually helped lead to the fall of the Roman state. 

But why, in the first place, did the army start to lose its dominance on the battle field, therefore requiring the hiring and using of foreign and barbarian troops?  By the end of the fourth century and into the fifth century, the Roman army had almost completely shifted from a professional “regular” army into a diversified non-citizen fighting force.  The army now saw a change from all heavy infantry to heavy cavalry, as numerous battles showed that even the strongest infantry could be no match for heavily armed cavalry out on the open plains (Roman-Empire.net).  As Rome never relied on cavalry because they did not have access to a steady supply of horses, they were forced to use allied and barbarian cavalry to do the job.  Eventually, the most effective army was one with light ground troops mixed with heavy cavalry.  The legionnaire, which was a type of heavy infantry, was now obsolete.  Though the Roman army did start to adapt to this new warfare, it never quite had the advantage over its adversaries again.  Conquered barbarians and other enemies all had equaled, if not better, fighting troops and experience in this area.  No longer were the imperial legions the preferred choice of troops.  The gradual change over to light and swift infantry and heavy cavalry eventually displaced the classic legion that once dominated the known world.

It was also common during this period for rogue generals and their loyal army or armies to betray the emperor and try to usurp power from the many territories or march into Rome itself.  This continuous change of emperors, some of which were not good leaders, started Rome on its downward spiral.  Eventually, in 284 A.D., the emperor Diocletian, who was made thrust into power by the army, was responsible for the start of the separation of the Roman Empire into the East and West segments.  By the middle of the fourth century, two definite East and West empires were formed, each with different capitals.  As the East and West sides each had a distinct culture and climate, the Roman military continued to lose a unified coherence, furthering its decline in power.