The Genius of Roman Military Organization

From Tarquinus to Trajan to Today

Genius (noun) [jēn-yəs, ˈjē-nē-əs] Etymology: Latin, tutelary spirit, natural inclinations, from gignere to beget 3 a: a peculiar, distinctive, or identifying character or spirit (-Merriam Webster Online Dictionary, 2009)

Throughout pre-modern history, most generals fought with whatever men and units they had managed to scrape up. Armies were organized by branches- cavalry, infantry, missiles, and support- if they were organized at all. Most had men grouped together by weapon type- spears, swords, axes, bows, but not all. The Spartans and the Macedonians came close to having an organizational base, but that was limited to their hoplites and phalanxes. Even the ancient Greek armies were barely structured- the phalangites in one big block, peltasts on the flanks, with some cavalry. The Germans and other barbarians were famous for coming to battle and lining up their men up with no regard whatsoever to what weapon they preferred. It was enough that these men chose to fight.

Even in the Middle Ages, there were few if any standardized armies. The warhost was called by the king, and his nobles brought their personal retainers and/or levies. From about 1100 onwards the rulers would demand specific numbers of troops from their lords, depending on the extent and wealth of their territories, but these were a far cry from the standardized and structured professional armies of the ancient world. Mercenaries - professional soldiers for hire - had some organization, but very little of it was standard. The Spanish tercios and Swiss pike formations were similar to legions and phalanxes in that they prescribed more or less specific combinations of troop types, but the organizational similarities ended there. Probably the most stringently structured military units of the Middle Ages were the military orders, such as the Teutonic Knights and the Knights Hospitallers, who, at least in theory, had to abide by very strict military codes of conduct which remained the same through the ages. It was not until the 15th century when gunpowder became prevalent on the battlefield that kings and dukes began to issue ordinances to set a certain standard for the equipment of all their military units. But very few lords commanded anything even approaching a standing army, and most troops were hired for single campaigns only. This could cause serious difficulties outside of the campaigning season, when unemployed soldiers would often roam the countryside, extorting friend and foe alike.

At the time of the Dawn of Rome back in 753 BC, Greek culture and warfare was the dominant force in the Mediterranean. Every civilization touched by them became influenced by them- including the wild and savage tribes of Italia. Greek ideas were discussed, Greek inventions sought after, and Greek warfare studied. Especially this last.

Rome at the time was divided into three tribes, and was ruled by a king. The king imposed a military levy upon the tribes, demanding each raise one thousand infantrymen and one hundred horse to the common army. Like the Greek citizen-soldier, these warriors would provide their own equipment and be levied only from among the freeborn. Naturally, only the wealthier citizens could afford the panoply of a Greek warrior, and thus to them fell the majority of the fighting. The Latin word for military levy was legio (to conscript), and thus the first legion was the entire army of Rome- not the fabled unit of later years. The legio was usually commanded by a praetor (lord) appointed by the king, and rarely directly under the king himself.

Although her armies were heavily influenced by Greek innovations, Rome was not Greece. Rome followed closely the Greek model to the point of blatantly copying it, and met defeat because of it when fighting in the Greek style upon the hilly terrain of Samnium and Etruria. Rome also had her own hereditary kings instead of elected leaders, one of whom was an industrious ruler whose tireless efforts had a major effect on Roman military ideas for centuries to come. This was Servius Tullius, who reformed the census, ordered the classes, expanded upon the Greek ideal for to citizen-soldiers, built the Servian walls around Rome, and many other deeds which we will ignore, during his forty-four year reign from 578 to 535 BC .

The Reforms of Servius Tullius

Like his predecessors, Servius Tullius called a levy when war threatened. Up to his time, the legion closely followed Greek ways- but Tullius was about to change that and introduce a purely Roman way. With organization and standardization. He did not want to create a warrior class as the Greeks were starting to do with their hoplites. He wanted a citizen army, like the Greeks once had, but one which remained true to the citizen soldier- a man who worked his farm or business during the year, then clad himself in armor to fight during the summer. A part-time warrior was less of a threat to the State, State Policy, and the king's rule, than a full-time warrior who sharpened his skills all year and wanted naught but to use them during the campaigning season.

So Tullius, displaying the typical efficiency and thoroughness for which Rome would become famous, took the citizen-soldier a step further. He organized the army, but more, he organized the whole of Roman society. He had a census taken, and on the basis of the numbers he received from the censors, had the populace divided into six classes. He then made demands upon each class to arm itself to a standard. His divisions also give us a look at the Roman population at the time.

The First Class consisted of eighty-two centuries. The top eighteen centuries were given sums with which to buy horses, which were then quite expensive animals but very necessary if one wanted cavalry. These became Public Horses, entrusted to those who would become the equites, or knights. The rest of the class was to be clad in bronze breastplates, helmets, greaves, and carry the round aspis of the Greek hoplite. They were armed with spears and swords as were the hoplites.

The Second Class, less wealthy, would have the same obligatory armaments, but were released from wearing a breastplate and round shield, but had to have a long Italian shield- the scutum. The Third Class, even less wealthy than the second, could dispense with the greaves but also had to have the scutum. And the Fourth Class just had to furnish its own weapons- spears and javelins. There were twenty-six centuries in these three classes together.

The Fifth Class, the poorest propertied class, provided thirty-two centuries of slingers for the Roman legion.

The sixth class of Romans, the capiti censi, consisted of everyone else. They did not own enough property to be classified in the Five Classes, and thus were exempt from military duty as the norm of the time was that men who had something worth fighting for, would fight well while those with nothing had nothing to lose.

These classes formed the basis of the legion, and were levied as needed. After the campaigning season ended, the men would return to their holdings and carry on with their normal life. This also conformed to the norms of the time. Servius Tullius also made one other decision regarding the levy- it was to be subdivided into two parts. The junior centuries consisted of family men in their prime, suitable for fighting. The senior centuries were men past their prime, and were more suitable for garrison duties.

The Servian legion otherwise remained true to the Greek model. Rome won her share of battles, but lost a fair share as well. Yet Roman power grew with the new army, and destroyed Etruscan power in the peninsula. During this time, Romans threw out their kings and began electing their own praetors, eventually replacing them with the consul.

To be honest, Rome often lost battles against foes she met for the first time. The Greeks, the Etruscans, the Gauls, and later the Carthaginians, the Germans, the Britons, and others. Yet Rome eventually overcame these foes, mainly because her generals and leaders had the space to trade for the time needed to analyze these new enemies and work up a viable counter. The Romans shamelessly copied what worked well, and improved upon those things that did not work so well.

Then Rome lost two big battles in a relative short space of time- against the pilum-casting Samnites at Caudine Forks (321 BC) and again against the sword-wielding Gauls at Allia (390 BC). The latter took Rome herself, but eventually left once they acquired the spoils they demanded and the threat of Camillus loomed- for Marcus Furius Camillus (446 - 365 BC) had an army with him and a reputation as a worthy warlord.

Camillus and his Reforms

Camillus and his successors were impressive military innovators. This has to be taken in plural, as a large part of the reorganization that occurred took place well after Camillus was dead. These visionary generals veered Rome away from the Greek model for good, toward a war machine that would conquer a continent. And they did it with that typically Roman thoroughness and organization.

They saw how poorly the phalanx legions of Tullius fared on uneven ground- of which Italia had plenty- and saw how effective the swordsmen of the Gauls were in breaking the Roman phalanx. They saw the possibilities of bringing that power to Rome, and acted upon it.

The first thing they did was do away with the old phalanx almost totally- it shrank down from three thousand phalangites to six tired centuries of triarii per legion- spearmen of the last resort. All other warriors were to be of a new sort- the hastati, the principe, or the skirmishing velite. The first two were to carry the Italian scutum for protection, and the Spanish sword (gladius iberius) as its main weapon. In homage to the Samnites, they would also carry a brace of pila. The equipment demands of the classes were dropped, and the new weaponry demanded of everyone, regardless of class. The basis was now no longer upon wealth or income but rather upon age and experience- the younger, inexperienced warriors became hastati while the older veterans principes.

The next thing done was to couple the centuries together to form maniples, though the names of the two centuries (prior and posterior) were retained. The prior century in the maniple would elect a centurion to command it. This centurion would then appoint a centurion to command the posterior century. Each maniple received a standard, upon which could be hung awards and honors won by the maniple, and a signifer to carry it. Along with the signifer was a cornicen, a horn-blower, whose purpose would be to call the attention of the maniple to the standard, and the standard bearer would face the standard in the direction of movement. This combination allowed the maniple to move as a complete unit.

They then established thirty maniples per legion, naming this unit as such for the first time. The Roman Army was to consist of a legion of Romans coupled with a legion of allies, under the command of the consul. Later, each consul had such an army, and they took it to war as a team, thus the Army consisted of two Roman legions and two allied legions. The Public Horse was replaced by Equites organized in turmae, but numbers and organization remained the same.

The command structure of the legion was also reformed. The legion still had no commander per se, being under the command of the consuls as part of a larger whole, yet command was implemented through the twenty-four elected military tribunes assigned to the army. These were usually assigned six per legion, but none of the six was designated the commander- command rights were still exclusive to the consuls.

This new army met with more success than loss. It would have met with far more success had it not been confronted by the military genius Hannibal Barca while itself being commanded by dolts who thought all they had to do was bring the army to battle and let the legions 'do their thing'. Having two commanders was like having a horse with two heads- never a good thing. Look at Cannae (216 BC) - Lucius Aemilius Paullus wanted to avoid battle, but Gaius Terentius Varro insisted. It being his day to command, he attacked. The result- Paullus died on the field with about eighty thousand of his men, while Varro escaped to a life of despised infamy.

The misfortune of facing Hannibal did not help the new legion any- Barca's genius lay in analyzing his foe's organization and using tactics that negated its strengths while attacking its weaknesses. Two of his three great victories lay in destroying the legions before they got into battle array- as in the ambush at Lake Trasimene - or flanking it with an ambushing force and thus negating its frontal power - as at Trebia. The third and greatest- Cannae- saw him use effective maneuver against an useless commander who allowed his army to be drawn into a bulge then get pressed from the flanks and rear. That disrupted the Roman formation and hindered its strength. The Numidian cavalry charge into the rear sealed the battle.

The Romans fixed the command problem thereafter by passed a law saying one consul always had to remain in Rome to govern while the other led the armies in the field. The four-legion consular army was now a fact. And the son of the consul killed at Cannae led this army against the Macedonian phalanx at Pydna in 168 BC where he thoroughly trounced the phalanx and proved the supremacy of the legion over the phalanx once and for all.

The Marian Reforms

Sixty years and many innovations later, the Camillan legions were becoming outdated. New enemies and new tactics had evolved, forcing the Romans to do the same. Yet Rome resisted, and when the Cimbri destroyed three armies in as many battles, she ran out of men to field her armies with. Along came Gaius Marius (157-86 BC), who perfected the Camillan legions by simplifying them and opening the ranks to all freeborn Romans regardless of economic class.

His reforms are discussed in detail in another article, so here we shall concentrate on the organizational reforms Marius introduced. But since he did open the recruiting to all freeborn, regardless of class, he now had to train as well as equip all of his soldiers, and do it fast. Thus he standardized the training and equipment and settled on the powerful principe as the model. All other troop types would form auxilia.

Just as the post-Camillan legions had coupled two centuries together to form the tactically-superior maniple, Marius coupled three maniples together to form the cohort. Cohorts had been used earlier, but were flexible administrative units, not tactical ones. The same pressures that demanded the formation of the maniple now surpassed that need and urged the formation of a standing cohort for battlefield use. Thus each legion was comprised of ten cohorts of legionaries- all of whom were now heavy infantry swordsmen.

The Rise of Professionalism

Gaius Julius Caesar- and above all Gnaeus Pompeius Magnus- made extensive and exhaustive use of personal lieutenants in the first century before the Common Era, both on the battlefield and as governors. Pompeius even went so far as to remain near Rome while he was governor of Hispana- governing through his lieutenants. These lieutenants were known as legates, and were invested with imperium in order to command the legions assigned to them. Legions still fought as parts of armies, but in this era they also began to operate independently with auxilia and were commanded by a legate.

Later, as the Empire was born and things began to settle, the Imperial Legions began to take shape. Each was commanded by a legatus legionis, the position now being made permanent. Assisting the legate were six tribunes as in previous legions. One of these was the tribunus laticlavius, the second in command of the legion and a legate in training. The other five were tribuni angusticlavii, professional officers.

The legion's third in command was not a tribune, but rather the Praefectus camporum- the camp prefect. He commanded all the surveyors, armorers, farriers, muleteers, artillerymen, engineers, medics, musicians, and everyone else who supported the legionaries. These extras were called immunes and were not required to perform the normal fatigue duties of the legionaries.

Later, smaller palatinae legions of fast-moving highly mobile troops were created, but they are beyond the scope of this.

How effective was this organization? From the Tarquin kings through Trajan we have seen them conquer and pacify western Europe, Southern Europe, North Africa, and the Middle East. They conquered and absorbed the Gauls, the Carthaginians, the Greeks, the Macedonians, the Dacians, the Numidians, the Spaniards, the Illyrians, the Armenians, the Batavians, the Britons, the Venetii, The Noricans, the Raetians, Pontus, the Egyptians, the Jews, the Arabs, and the Pirates of the Mediterranean, just to name a few. And they kept it running until the Crisis of the Third Century.

To Today

But the title of this article is the Genius of Roman Military Organization from Tarquin to Trajan to Today. Why today? Rome no longer exists as a world power. But the spirit of her military organization is still alive and well in the United States Army.

It may be only coincidence that the American infantry division is a 21st century version of the early Imperial Roman legion, but then again, maybe not. It is known that some medieval lords modeled their armies upon Roman methods, using Roman drill to perfect their discipline and ability to deliver optimized volleys. But their organization was implicitly late medieval- where infantry was slowly coming to join the horse in combat power. The modern American Army and the Roman legions have very close ties, and it is pretty certain that the American Army was not modeled upon the Roman Legions, but evolved as had the legions into a world-class power.

Evolved? Yes, armies evolve. Needs, experiences, and above all technological innovations dictate a need to adapt to the modern battlefield. The gladius and scutum removed the phalanx from history, then cavalry evolved to make heavy legions obsolete. Pikemen and gunpowder reduced the power of cavalry, the bayonet made massed infantry unstoppable, until machine guns reduced the waves of infantry to suicidal walks through lead rainstorms. Tanks rendered machineguns useless, and fighter-bombers made tanks rolling coffins. As technology and weaponry advance, so does organization. And the organization of the United States Army and the Romans Legion followed an eerily similar path though millennia apart.

So either warfare has not changed all that much in two thousand years, or the systems are similar because they both work well. Having studied American military development as well as Roman, it seems the two evolved independently due to separate and unique pressures, but the end result is surprisingly similar. Amazingly enough, so are the stages in reaching that result.

Innovations and technology improve at a geometric rate. Where once technological steps took hundreds of years to accomplish, now they can take decades or years or even months. The automobile as commercial personal transportation began a hundred years ago with a vehicle that horses could outrun. Today we can drive from Amsterdam to Fredrikshavn on the tip of Denmark in less than eight hours. Or fly there in two hours.

Likewise, armaments moved on from clumsy flintlock muskets in Wellington's time to Minie-balls of the American Civil War to the repeating rifles of the Wild West to the machine guns of World War I- a mere hundred years. We moved from horse-drawn artillery in the First World War to tanks and jet fighter planes in the Second World War- a mere twenty years.

It took Rome nine hundred years to evolve from the phalanx legion of the early days to the Imperial Legion. It took the Americans two hundred years to do the same. The standard American unit in 1776 was the regiment of one thousand men who fought in small clusters of regiments- very much like the legion of the Roman Kings.

The regiments were quickly grouped together into brigades of five- which were themselves grouped into corps of four- making a consular army of about twenty thousand by the time of the American Civil War.

The Modern Mechanized Infantry Division

Today's American infantry divisions are commanded by a major general and his staff, consist of ten combat battalions (each of three combat companies and comparable to the cohort, each company roughly the size of a maniple). The division is supported by many and varied smaller units of supply (fabri), transport (muleteers), artillery (onagers), medics (medicus), signal (cornicen and signifers), maintenance (armorers and farriers), scouts (cavalry), engineers, and others, under the command of the Assistant Division Commander for Support, who is a brigadier general and third in command of the division- much like the Praefectus Camporum.

Nowadays, the Americans are moving into lighter, more mobile units that can be deployed anywhere a crisis emerges, such as the 173rd Airborne Brigade, the 82d Airborne Division, the 101st Airmobile Division, the 10th Mountain Division, and others. This parallels the evolution towards the palatine legions.


This unconscious similarity of development and organization leads one to believe that whatever spirit inspired the Romans is still around, fifteen centuries after Rome herself fell. Rome's genius lay in seeing what works and adapting it, or devising new innovations to solve specific current and future problems. Her organizational aptitude was amazing for its day, and set a standard that had not been matched for two thousand years. Evidently the Romans did it well - two thousand years later, our modern armies are organized quite similarly to their ancient counterparts.