The Roman legions are impressive for their
historical achievements but rarely do we stop to properly understand their
nature at a fundamental level. How were they organized? What
was their leadership structure? How large was their logistics train?
What was their frontage in battle? Today let’s explore the True Size
of a Legion of the Roman Empire. Our team spends a lot of time producing video
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clicking the link in the description below enjoy The foundation for the Roman legion was the
legionary. These soldiers were Roman citizens who were drawn from across the general
population. Potential recruits had to meet certain criteria and pass a series of tests.
According to Vegetius the ideal candidate was a rural man from a temperate climate who stood
about 6 roman feet tall. Upon taking their oath and undergoing 4 months of training they
would be ready to join the legions for battle. Whilst in service each soldier would
be assigned to a group of tent mates known as the Contubernium. While there is some
debate, most academics agree that it consisted of 8 legionaries in addition to 1-2 military
slaves, 1-2 mules depending on supply needs, a millstone, and a standard A-frame
tent. It is with this Contubernium that a legionary would spend most of his
time. This brotherhood was so ironclad that the term contubernalis emerged in the
Latin vernacular as a term for comradery. When the legion encamped, each Contubernium
functioned as its own self-sustaining unit. For instance while the slaves pitched the
tent, the younger legionaries might be sent to fetch fodder and firewood for
the campsite as others prepared food. Grinding the grain ration in particular was
a labor intensive task which occurred every night. This grain was most often used for bread,
biscuits, and porridge which served as the staple for the average legionary’s diet that was further
supplemented by salted meat, vegetables, cheese, wine, and olive oil. When not performing essential
duties, the members of a contubernium would make the most of their off time. This included
things like gaming, gambling, and relaxing. When it came time to move, a Contubernium’s
gear would be efficiently loaded for transport. Each soldier carried roughly 20 kg of arms and
armor in addition to their entrenching tools, bedroll, rations, and personal items. The
heavier gear such as the tent, stakes, mill stone, and various other items
would be loaded onto the unit’s mule. Yet while the contubernium was self-sustaining
in a day-to-day sense it was not a functional military unit that could hold its own in battle.
For this purpose 10 Contubernia would be grouped together into a Century for a combined total of
80 legionaries, 10-20 slaves, 10-20 mules and 11 tents. In keeping with its battlefield role,
the Century was assigned a series of officers. The Centurion was the commanding officer, the
Optio was his second in command, the Tesserarius was third in command and watchman, the Signifer
was the Standard Bearer, and the Cornicularius was the trumpeter. These men in turn had their own
support staff, mules, tents, and other belongings. The officers were critical as the means
by which the men of a Century were made a part of the Roman legion as a whole.
When it came to discipline and training, the commanding Centurion and his Optio proved
integral to maintaining a well drilled unit through their use of disciplinary staves,
the vitis and the hastile respectively. When it came to performing duties
the Cornicularius helped summon the men for roll-call, review, and
for the march while the Tesserarius distributed the watchword and
managed those on sentry duty. And finally when it came to fiscal management,
the Signifer was in charge of a unit’s finances while the Cornicularius was in charge of the
military clerks. It was these men who tracked a soldier’s pay and all of the deductions they
had accrued. In this regard it is estimated that around 2/3rds of a legionary’’s yearly salary
went towards food, clothing, and common expenses. On the march, a unit would be led by its
Centurion, Signifer, and Cornicularius while the Optio and the Tesserarius likely brought
up the rear and maintained the order of march. In battle the same order appears to have
been maintained with the senior commander leading from the front-right and his deputies
policing the formation. The exact position of the Signifer and Cornicularius is debated
with some arguing that they were in close proximity to the Centurion for ease of
command while others place them further back for reasons of safety and maintaining
combat effectiveness of the front rank. As the Romans of the Republic had found, while
a unit of around 100 men could hold its own in battle, its strategic uses were limited. Thus
the Cohort was born as a way to combine six Centuries into a large group of men who could
have a more substantial role on and off the battlefield. In total a standard Cohort had
480 legionaries, 30 officers, 60-120 slaves, 60-120 mules, and around 66 tents. There are some idiosyncrasies of the Cohort
that are worth mentioning. The prestigious First cohort of every legion was made of 5 double
strength Centuries for a total of 800 legionaries. Typically these were the veterans of a legion, its
iron core, which inspired and offered an example for the more junior soldiers of their fellow
Cohorts. As such, it was the unique honor of their Aquilifer to carry the Legionary Eagle into
battle. This venerated standard represented the soul of the army, being kept in a dedicated shrine
at the heart of a legionary camp or fortress. The Augustan reforms standardized the size,
number, and position of the legions across the Empire. Therefore it was actually
quite rare to see legions moving around in their entirety outside of major campaigns.
Instead the Cohort was the typical operational sub-group which could be dispatched for
all manner of duties. For instance it might be sent out to reinforce key areas, build
infrastructure, or to respond quickly to threats. This group was largely self-sustaining,
underscored by the presence of Cohort camps in archaeological records - which are significantly
more common than legionary fortresses. When the need arose, one or more Cohorts were
grouped together into ad-hoc units, known as vexillationes, effectively a legion in miniature.
These were the most common "strike force" in the Roman Empire. Often two cohorts would be sent
out under a single commander, numbering about a thousand men, which could effectively
solve any problem quickly and efficiently. The largest and most iconic standard Roman force
was the Legion. It was composed of 10 Cohorts, with a theoretical paper strength of
about 5,120 soldiers. Using the upper end of our prior figures, these would
also bring with them about 295 officers, 1400 slaves, 1400 mules, and around 660 tents. But a Legion had even more elements worth
mentioning. For instance Josephus tells us that during the early Principate each
legion was assigned a cavalry unit which epigraphic evidence suggests
was called the Equites Legionis. Likely these served as scouts and bodyguards at
the direct disposal of the General. They were 120 troopers strong, which were likely
broken down into four 30-man Turmae. In a parallel structure to the infantry century,
each Turma had a commanding officer, the Decurion, two sub-officers, the Duplicarius and the
Sesquiplicarius, as well as a standard-bearer, the Signifer. These riders had 1-2 spare
horses while their gear was carried by an estimated 60 mules and drivers with the cavalrymen
themselves being housed within around 15 tents. Furthermore, legions were assigned an artillery
corps. Estimates vary, but it is generally accepted that each century had one small scorpion
for a total of 60, while on major campaigns each Cohort was assigned a medium ballista for
a total of 10. Additional siege equipment such as rams and large onagers were added as
needed but we have assumed a mix of 5 pieces. Crewing, maintaining, and transporting such gear
would have required a substantial siege train. No reliable records exist but we can
approximate the use of at least 15 4-oxen carts laden with the components
of the medium to large siege pieces, while the smaller scorpions were carried
by a mule from their respective century. Tending to the artillery and all the other
engineering needs of a Legion would have been the Fabri. These were the members of the Engineering
Corps whose numbers are not defined but may have been counted at around 10 specialists, 1 per
Cohort, whose expertise enabled them to supervise the work of general laborers. Another critical
group would have been a Legion’s Medical Staff. Once more we have no firm numbers and will
therefore assume 10 doctors, 1 per Cohort, with an additional 20 assistants, 10 2-horse
ambulance carts, and 10 medical tents. And last but not least among the support staff
would have been the legion’s scribes which we will estimate at around 15 men with 15
supply mules. While often overlooked, these scribes were key to the
institutional integrity of a legion. They maintained the records of the force,
which included everything from pay rolls to service logs, supply tallies,
reconnaissance reports, and more. Beyond this a legion would have had all manner
of spare parts, food, personal belongings, and other items in need of transport. Without
any explicit records, we will assume this would have been carried by around 50 additional mules
for a grand total of approximately 1,600 such animals. That's almost 1 mule for every 5 men
in the legion. But the ratio of animal to human rises even higher when you consider the herds
of livestock which would have been shuffled along an army as a ready source of food. We will
not be modeling these in this particular video. Commanding this behemoth of a force
were a series of high ranking officers, the Legionary Legate, the Camp Prefect, 6
Tribunes, and additional musicians and standard bearers. These along with the various sub-officers
formed the all-important hierarchy of a legion. It will now be worth discussing
their ranks in greater detail. We will begin with the Centurions, of which there
were 1 per century and thus about 60 per legion. But not all were created equal. A strict ranking
system was in place which had its roots in the traditions of the manipular armies from the
Republic. In order of highest to lowest rank this resulted in the following Centurion titles:
the pilus [peel-oos] prior and the pilus posterior who commanded the first and second centuries
respectively. The princeps [prin-keps] prior and the princeps posterior who commanded the third and
fourth centuries. The hastatus [ha-stah-tus] prior and the hastatus posterior commanded the 5th
and 6th Centuries. Between Cohorts, the officers of the 1st Cohort were the most senior while
those of the 10th Cohort were the most junior. It should also be noted that the prestige of the
1st Cohort’s Centurions was recognized in that its 5 officers were known as the Primi Ordines,
the most senior of which was the Primus Pilus or first spear. This was a highly coveted post,
typically lasting only a single year, and would be the crowning achievement of a long career
in the army. Over time as the legions settled down into fixed positions, the role of the Primus
Pilus would evolve to become more administrative. But beyond these career Centurions, most
legions were commanded by non-professional Legates selected from the Senatorial class.
Some exceptions did exist such as the Legio II Traiana which was commanded by an equestrian
prefect. Whatever the case, the Legate or Prefect would have 6 Tribunes serving directly beneath
them. In the Republican period these had also been non-professionals drawn from the political
elite but during the Principate the 5 tribuni angusticlavii or the Narrow Stripe Tribunes could
also be promoted up from the Centurion ranks. In contrast the singular tribunus laticlavius
or Broad Stripe Tribune was typically still a young man of the senatorial class who
only served with the legion for a year before returning to his political career.
Together these Tribunes provided important tactical command of a legion during wartime
whilst otherwise acting as administrators. Let’s now take a moment to step back and
appreciate the real size of the legion in its various forms. We can begin with a hypothetical
parade rest of the entire force and its gear. Together they cover 25 square
kilometers and number about 9,000. Of all the beings within this area 80% are
humans and 20% are animals. Among the people, 73% are infantry or cavalry, 4.5% are officers,
0.5% are specialists, and 22% are military slaves. But this sort of a deployment is quite a-historic.
More commonly you would find a legion in their camp, on the march, or in battle. Let’s take
a look at the True Size of each of these. One of the most typical places to find a
legion would be its home base, the Castra Legiononis. These permanent positions had begun to
be established during the reign of Augustus as a means to begin fortifying the Empire’s various
frontiers. But while they did boast moats, walls,and towers they were not intended to
serve as impregnable military hardpoints. Rather their purpose was to serve as the
staging point for offensive action. They were a place for the legions to muster, gather
supplies, and oversee their area of operations. As such these bases were well
equipped with facilities ranging from administrative buildings, to barracks,
hospitals, granaries, armories, and more. Overall their arrangement was quite regular
but with dimensions which stretched as needed. For our example we assume a fort measuring about
470 by 470 meters. For perspective this is 220,000 square meters or about 55 acres which is
the rough equivalent of 23 soccer fields. Based on our records it was actually quite rare
for a legion to be at its base all at once. Much of the time, soldiers would have
been dispersed on leave, on watchduty, or on all manner of other missions.
Only for major campaigns would an entire legion be assembled. And, when the
time came, they would march out for war. This would have been done in a disciplined
manner. Generally speaking a legion deployed in the following order: the scouts, the
vanguard, the officers, the main legionary body, the impedimenta or baggage train, and the
rear guard. There are many nuances we could get into but this description
will have to suffice for now. For this depiction we have modeled our
previously described legion on the march with a maximum of 6 men abreast. This assumption
is consistent with the widest of Roman roads which measure around 6 meters across. In this
arrangement, the entire column of about 7,200 men and 1,900 animals stretches out over
1.9 km. At a walking speed of around 5 km/hr, it would take 23 minutes for a single
legion and its baggage train to pass. At a gallop, it would take a rider going
40 km/hr about 3 minutes to ride across the entire length of the column. But this
assumes quite idealized conditions. If roads were narrow and progress delayed for any reason,
a single legion could easily double in length, stretching well over 3.8 km, taking 45 minutes to
pass, and requiring 6 minutes to ride from back to front. It's no wonder an army in such a formation
was highly vulnerable whilst on the move. But assuming no attack took place, a legion
would strike camp each night in its journey across the lands. In this way it would
slowly advance into enemy territory. When battle was eventually to be joined,
a legion would now deploy for combat While armies of the Republic tended to
deploy in the standard Triplex Acies, those of the Empire were far more flexible.
The exact manner in which legions might be deployed would depend on the situation
and the preferences of the commander. Almost universally however they would
still have honored the prudent idea of troops being deployed to the center, the
wings, and most importantly the reserves. For this example we have assumed that in a vacuum
our single legion has adopted a Republican style triplex acies. Here the 2,000 soldiers of Cohorts
7 through 10 form the first line, the 1,500 soldiers of Cohorts 4 through 6 form the second
line, and the 1900 soldiers of Cohorts 1 through 3 with the cavalry form the third line to defend
the rear and act as an emergency reaction force. Zooming in, I will note that most scholars
agree that soldiers in a unit stood 1 meter side to side and 2 meters front to back.
Assuming a typical century is arranged in 8 ranks of 10 men it occupies a space of 16 by 13.5
meters. Additionally if we assume that multiple centuries maintain 2 or 3 meters of separation
side to side and 8.5 meters front to back, we are left with a total formation whose frontage
is about 609 meters across and 138 meters deep. To contextualize this, we can state that it would
take a soldier about 4 and a half minutes to walk across the front and a rider about half a
minute to make the same trip at a gallop. An archer with an upper bow range of
200 meters could only fire across 33% of the legion’s frontage. For someone
looking across this same distance, a human sized figure on the other end would
be quite difficult to discern. The logistical implications of all this are certainly relevant to
the experience of being on an ancient battlefield. And yet we must also keep in mind that
the most important battles of the Roman era involved far more than a single legion
and that the entire Empire at its height had at least 30. Thus you must take all the figures
we have shared in this video and multiply them many times over to even begin to wrap your
head around the scales we are talking about. For now though, I hope that this explanation
has at least given you a basic understanding of the subject and the value of putting such
matters in their proper spatial context. Stay tuned for additional videos
where we explore the True Size of our past and let us know what topics
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