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When would the rank of Praefectus be used in the Late Roman Army
#1
Hi All,
 
So my first post on this website. ?
 
I have a query concerning the rank structure of the late roman army (284 – 476 AD), specifically concerning when the rank of Praefectus would be used. (I believe this rank would ‘roughly’ sit above the senior centurion of a cohort, and below the commanding Tribune of a legion)
 
Historically I understand that the rank of Praefectus is descended from the rank of ‘Praefectus Castrorum’ or Camp Prefect, the third highest ranking officer in a Roman Legion after the commanding Legate and Tribune, and responsible for looking after the roman legionary camp and equipment.
 
First, a little background to set the context of this thread.
 
I’m currently in the process of writing a historical fantasy novel that depicts an extra-dimensional invasion of the Roman Empire and its neighboring kingdoms in the late fourth century AD by an race of Orc-‘ish’ invaders armed with early-mid gunpowder era level technology. (With some magic mixed in for good measure)
 
While fictional, as this book will feature the real-world Roman Empire of the late fourth century AD I wanted to make this depiction as accurate as possible in terms of the ranking systems and organizational structure used within the Roman army.
 
I’m not a qualified historian, however I do have a special interest in the Roman Empire and so I do have what I’d consider to be an above average knowledge base of this era.
 
This being said, I did make a few assumptions on the size of standard late roman army units and the officers who would command them that I’m now reevaluating, hence this post.
 
Firstly, I’m aware that the old system of Legions and Auxiliary Cohorts established by Augustus in the 1st Century AD was heavily reorganized by Emperor Diocletian and later Constantine, with the army being split between the Limitanei (Border Legions) and Comitatenses (Field Legions), whilst both Emperors of the East and West maintained their own Escort armies comprised of elite Palatini (Palace) grade troops. (At least in theory. In practice as I understand it these units would be frequently mixed and disbanded into field armies as Roman Emperor’s and the General’s they appointed periodically pulled troops for defense or campaign from wherever there were troops available to pull from)
 
This novel will largely revolve around a cohort (and its officers) of Limitanei based at the Romano-British fortress of Arbeia in 376 AD. For anyone unfamiliar with this real-world location, Arbeia was the eastern most fortress of Hadrian’s Wall, originally built around 160 AD as a standard auxiliary fortress containing a garrison of about 600 men.
 
What I’m currently unsure about is what specific rank of officer would command a garrison of a standard auxiliary fortress of this size.
 
Initially (for some reason) I made an assumption that the maximum sized ‘permanent’ unit of the Late Roman Army would have been a Cohort, 600 men strong for the Limitanei (infantry and cavalry) and a double strength Cohort of about a thousand men for a Comitatenses field legion. In both cases my understanding was that these battalion and regimental sized formations would fall under the command of a Tribune, with several such garrisons or double strength field Cohorts being grouped together into a border army or field army under the command of their respected Dux (Duke) or Comes (Count).
 
However, having done a little further research i understand now that a legion of the Late Roman Army typically consisted of a minimum of 2 Cohorts, the first of which would be double strength. As a result late roman Legions for both the field and border armies would typically number between 1000 - 2000 soldiers under the command of a Tribune, with a centurion acting as commander of each Cohort.
 
My understanding is that the Cohort occupying Arbeia would be under the command of a Senior Centurion (Primus Pilus), however for simple story telling perspective I would prefer the commander of this garrison to be an officer of above Centurion rank, but I’m guessing 600 men on paper would be beneath a Tribune’s remit to command.

To provide further context on why I’d like the commander to hold a rank superior to Centurion, this is because his subordinate (a major character for the first half of the book) is a Centurion. While a Cohort would have a minimum of 6 centurions, from a story telling view I find it a lot easier to right interactions between characters whose ranks are not nearly identical.


With this in mind, would I be could correct in theorizing that a former auxiliary fortress built for a standard strength Cohort (600 men including a cavalry contingent) could be commanded by a Praefectus? 

 
This would in my opinion make sense as Praefectus would be ‘master’ of a camp, such as an auxiliary fortress.
 
Thank-you for any assistance you may be able to provide in advance, and kind regards
 
Tim
Real Name: Tim Hare
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#2
(10-13-2019, 08:22 PM)RogueDragon2010 Wrote: the rank structure of the late roman army (284 – 476 AD)

Hi Tim!

This is a huge subject, and one which has been discussed a great deal by historians over the years without too many firm conclusions. I'll try and give you some general ideas here though... [Image: smile.png]

First, you may find these two web articles useful:

Hierarchy in the Late Roman Army, 300-550AD, by Robert Vermaat of Fectio.

The Roman Army of Constantine, Part 2, which focusses on rank structures and changes.


(10-13-2019, 08:22 PM)RogueDragon2010 Wrote: This novel will largely revolve around a cohort (and its officers) of Limitanei based at the Romano-British fortress of Arbeia in 376 AD... What I’m currently unsure about is what specific rank of officer would command a garrison of a standard auxiliary fortress of this size.

Luckily there is a firm answer to this question at least. The Notitia Dignitatum (a list of offices and military units dated to some time between AD395 and AD420ish, probably drawing on earlier material too) has a section on the command of the Dux Britanniarum, which notes that one of his officers is the Praefectus numeri barcariorum Tigrisiensium at Arbeia.

So the garrison in the late 4th century was the Numerus Barcariorum Tigrisiensium, and they were commanded by a Praefectus. You might be interested in this article about the Barcarii written by Francis Hagan.

However, a numerus was (probably) not the same thing as an old-style cohort. The word was used to describe all kinds of late Roman units, from cavalry squadrons to legions, and seems to have connoted no set number of men. If you can bear to pick through it, the thread on Late Roman Unit Sizes will give you an idea of the range of theories on this.

There are other limitanei units listed in the Notitia that are called cohorts though, and in some cases these occupy the same garrisons known in earlier times. Unlike the old auxiliary cohorts, most are commanded by tribunes. However (nothing about the late Roman army is easy!) some of these 'cohorts' occupy forts far too small for c.600 men; in fact, some of the new fortifications on the Danube, home to 'cohorts' in the Notitia, would only hold between 60 and 120 men.

Also, some of internal buildings of the Hadrian's Wall forts seem to have been redesigned in the 4th century to accommodate a smaller garrison.

We might guess, then, that the numerus at Arbeia resembled an old-style cohort, but was perhaps rather smaller. The 'praefect' in command might have resembled an old-style cohort commander, but could have been a promoted centurion-level officer (see below for ranks!), or even a local leader given a military command (take a look at Rob Collins's Hadrian's Wall and the End of Empire for some discussion on these kinds of changes).


(10-13-2019, 08:22 PM)RogueDragon2010 Wrote: the maximum sized ‘permanent’ unit of the Late Roman Army would have been a Cohort, 600 men strong for the Limitanei... i understand now that a legion of the Late Roman Army typically consisted of a minimum of 2 Cohorts

There is a widely-held theory that the smaller 'mini legion' (c.1000 men) of the late empire was formed originally from the two-cohort vexillations (detachments) used in field armies of the tetrarchic era. This might be the case.

However, the evidence of an almost-complete legion rank listing from Perge, dated to c.AD500, suggests that late Roman legions had a decimalised rank structure, with (in that case) 20 centurion grade officers, rather than the 12 or so we would expect if the unit was made of two old cohorts.

This long thread about the 'Legion of Perge' might prove interesting. The inscription is contentious, but does at least give a full list of ranks, which would probably have been in use in the 4th-5th centuries as well.

As a rough precis, these are the ranks I would expect for a limitanei unit c.AD400:

Tribune/Praefect/Praepositus - this would be the unit commander. What the differences might have been between them is obscure, but generally all field army units and most frontier 'cohorts' are commanded by tribunes, while frontier cavalry units and legions, and some 'numeri', are led by Prefects. Praepositi could lead either, perhaps temporarily.

Ordinarius - this was the centurion-grade officer of the late legions and limitanei. They may have commanded subunits ('ordines') of c.60-120 men, which may in turn have been called 'cohorts' (the late writer Vegetius claims that 'cohorts' had draco standards, like the old centuries, which might suggest that the old century had been enlarged and renamed a cohort. That might suggest that the 'mini legion' of c.1000-1200 men was divided into ten 'mini cohorts' of c.100-120 men, each led by an ordinarius - but this is all very hypothetical!)

Vicarius - seems to have acted as the deputy to the tribune. Perhaps also called Tribunus minor. Maybe a temporary rank?

Campidoctor - originally a drill master, by the later empire this guy had become the most senior soldier in the unit. Whether he was one of the Ordinarii, or a separate rank, is unknown - the Perge tablets mention campidoctores, but they aren't listed on the grades, which might suggest the former...

Augustales and Flaviales - these are senior soldier or NCO grades, and appear in both legions and limitanei units.

Armaturae/Semissales - senior soldier grades, of various sorts.

Besides these men, there was the Optio (who functioned more like a subunit clerk at this date), the signifer (standard bearer, aka draconarius), various musicians, and the munifices, or milites (common soldiers). A clerk called an actuarius turns up in some sources as well. Beneficiarii are listed on the Perge tablet and perhaps acted as aides to the commanding officer.

There was another rank structure in use in the Roman army, confined to the cavalry and the 'auxilia palatina'. This had the centenarius as the centurion grade, with a ducenarius above him and various grades of biarchus and circitor below him, plus an obsure higher rank called senator. How all this compared to the legion/limitanei ranks is anybody's guess.


(10-13-2019, 08:22 PM)RogueDragon2010 Wrote: My understanding is that the Cohort occupying Arbeia would be under the command of a Senior Centurion (Primus Pilus)

The Primus Pilus vanished some time in the later 3rd century (or rather, became a civilian job associated with tax gathering, I think).
Nathan Ross
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#3
(10-20-2019, 08:08 PM)Nathan Ross Wrote:
(10-13-2019, 08:22 PM)RogueDragon2010 Wrote: the rank structure of the late roman army (284 – 476 AD)

Hi Tim!

This is a huge subject, and one which has been discussed a great deal by historians over the years without too many firm conclusions. I'll try and give you some general ideas here though... [Image: smile.png]

First, you may find these two web articles useful:

Hi Nathan,

Thank you for the above links, and I can only apologize it’s has taken me so long to respond.

Funnily enough I did come across these 2 pages after posting this thread, but this helps regardless.

(10-20-2019, 08:08 PM)Nathan Ross Wrote:
(10-13-2019, 08:22 PM)RogueDragon2010 Wrote: This novel will largely revolve around a cohort (and its officers) of Limitanei based at the Romano-British fortress of Arbeia in 376 AD... What I’m currently unsure about is what specific rank of officer would command a garrison of a standard auxiliary fortress of this size.

Luckily there is a firm answer to this question at least. The Notitia Dignitatum (a list of offices and military units dated to some time between AD395 and AD420ish, probably drawing on earlier material too) has a section on the command of the Dux Britanniarum, which notes that one of his officers is the Praefectus numeri barcariorum Tigrisiensium at Arbeia.

So the garrison in the late 4th century was the Numerus Barcariorum Tigrisiensium, and they were commanded by a Praefectus. You might be interested in this article about the Barcarii written by Francis Hagan.

However, a numerus was (probably) not the same thing as an old-style cohort. The word was used to describe all kinds of late Roman units, from cavalry squadrons to legions, and seems to have connoted no set number of men. If you can bear to pick through it, the thread on Late Roman Unit Sizes will give you an idea of the range of theories on this.

There are other limitanei units listed in the Notitia that are called cohorts though, and in some cases these occupy the same garrisons known in earlier times. Unlike the old auxiliary cohorts, most are commanded by tribunes. However (nothing about the late Roman army is easy!) some of these 'cohorts' occupy forts far too small for c.600 men; in fact, some of the new fortifications on the Danube, home to 'cohorts' in the Notitia, would only hold between 60 and 120 men.

Yes I’d read up a little on the Numerus Barcariorum Tigrisiensium. I understand its thought this may have been some kind of naval unit whose origins were in the Tigris River region of the far east.

My understanding is that Numerus as a unit may have been a detachment of what the romans would consider ‘barbarians’ from allied tribes beyond the frontier who were integrated into the roman army, not unlike Foederati. At least that was the case during the earlier Imperial Period. (Before the 4th Century)

I also understood that it’s believed the roman units stationed in the North and West of Britannia were withdrawn around 383 by Magnus Maximus as part of an agreement with previously hostile tribes to support his ambitions in Gaul and Italy. If the ND dates from around 420 AD in the Western Empire, do you think its possible some of the garrisons being overtaken by ‘indigenous’ troops could have mainlined their original roman names, but whose designations changed? (e.g. a Cohort is down grounded to a Numerus, but keeps its original name – Or am I giving the Late Roman Army to much credit for its organizational skills and general ability to keep things consistent?)

Also, you wouldn’t happen to know if there is a list anywhere on the Internet of all roman army units listed in the ND and which specific regions they fell under and where they were garrisoned. (Something like the link you provided for Britannia, but for the whole empire)

Just thought it may be worth asking.

(10-20-2019, 08:08 PM)Nathan Ross Wrote:
(10-13-2019, 08:22 PM)RogueDragon2010 Wrote: the maximum sized ‘permanent’ unit of the Late Roman Army would have been a Cohort, 600 men strong for the Limitanei... i understand now that a legion of the Late Roman Army typically consisted of a minimum of 2 Cohorts

There is a widely-held theory that the smaller 'mini legion' (c.1000 men) of the late empire was formed originally from the two-cohort vexillations (detachments) used in field armies of the tetrarchic era. This might be the case.

However, the evidence of an almost-complete legion rank listing from Perge, dated to c.AD500, suggests that late Roman legions had a decimalised rank structure, with (in that case) 20 centurion grade officers, rather than the 12 or so we would expect if the unit was made of two old cohorts.

My assumption that a legion could number 2,000 men or over came from the historical novel ‘Legionary’ by Gordon Doherty. (It was a good book overall, but I think he takes a few liberties with history but overall, it’s no Gladiator from a historical accuracy standpoint)

A small author’s note at the beginning states that Late Roman Army legions typically numbered about 2,000 men split between 3 Cohorts (the first double strength), all of which were likely to be under strength. Despite this, I’ve not been able to come across any other consensus that give a Late Roman Army a strength of over 1,000 men on paper.

All ways seemed strange to me that a Late Roman Army legion on paper was almost exactly the same in size as the first Cohort of an earlier legion. This made me wonder if when most of these new legions were raised as or reformed as ‘mobile’ units the Roman government could only afford to raise and equip the first Cohort. Or if on the other hand the Late Roman Army was so pressed for manpower, then any subsequent Cohorts raised alongside the First Cohort were stripped for garrison duty while the first Cohort was transported to wherever it was needed.

(10-20-2019, 08:08 PM)Nathan Ross Wrote:
(10-13-2019, 08:22 PM)RogueDragon2010 Wrote: My understanding is that the Cohort occupying Arbeia would be under the command of a Senior Centurion (Primus Pilus)

The Primus Pilus vanished some time in the later 3rd century (or rather, became a civilian job associated with tax gathering, I think).

Oh Bugger!

Thank-you! ?

And again thankyou for taking the time to respond to me in the first place.

The feedback you’ve given here is invaluable!

Tim
Real Name: Tim Hare
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#4
(10-27-2019, 04:15 PM)RogueDragon2010 Wrote: My understanding is that Numerus as a unit may have been a detachment of what the romans would consider ‘barbarians’ from allied tribes beyond the frontier ... (Before the 4th Century)

Yes, that's the earlier definition. By around AD300 numerus (or the Greek equivalent arithmos - both words just mean 'number') was used increasingly for newly-raised army units, both cavalry and infantry. By the late 4th century it was synonymous with 'military unit' and was used for everything from cavalry squadrons to legions.


(10-27-2019, 04:15 PM)RogueDragon2010 Wrote: roman units stationed in the North and West of Britannia were withdrawn around 383... If the ND dates from around 420 AD... some of the garrisons... could have mainlined their original roman names...?

A knotty question! Exactly who might have withdrawn troops from Britain, and when, and whether any came back again afterwards is pretty impossible to determine. Maximus may have taken some, Stilicho may have taken some more (but maybe introduced a new central field army under the Comes Britanniorum), Constantine III may have taken much of the remainder (or just the field army troops).

The ND list is probably based on the situation some time in the later 4th century, perhaps with additions from c.AD400. I would think it a safe bet that most of the units listed would have been present in the last quarter of the 4th century. It's also probably safe to guess that unit sizes would have been much reduced, especially in the aftermath of whatever chaos was going on c.AD367-69...


(10-27-2019, 04:15 PM)RogueDragon2010 Wrote: a list anywhere on the Internet of all roman army units listed in the ND and which specific regions they fell under and where they were garrisoned.

Yes! Luke Ueda-Sarson's excellent site had detailed listings for all the military commands in the ND (scroll down for the 'Western Empire', and further down for an alphabetical list of units).


(10-27-2019, 04:15 PM)RogueDragon2010 Wrote: seemed strange to me that a Late Roman Army legion on paper was almost exactly the same in size as the first Cohort of an earlier legion. This made me wonder...

You're not the first person to notice that!

However, the 'double strength' first cohort may not have survived the upheavals of the third century (or the departure of the primus pilus?). An tomb inscription from Sitifis in North Africa to signifer Aurelius Vitalis of Legion III Italica (AE 1967, 00639b) mentions that he's serving with a vexillation comprising cohorts I and II. The same place has a mithraeum built by men of cohorts X and VII of Legion II Herculia - these were probably legion vexillations of the mobile field force of Augustus Maximinian, operating in North Africa in AD298. So the first cohort was, it seems, the same size as the others by the end of the third century...

As these two-cohort detachments turn up quite often though, it seems likely that they might have been the ancestor of the later 'mini legions', rather than the old first cohort, or the auxiliary cohors miliaria.

My hypothesis would be that these detachments, originally comprising two cohorts of 480 men each, were merged into one large unit of 960 men and then subdivided into ten new 'mini cohorts' of 96 men, each commanded by an ordinarius. With officers included the new unit would be close to a thousand men. At some later date (under Constantine or his sons?) new senior soldiers named Augustales and Flaviales were introduced, bringing each 'mini cohort' up to c.120 men, and the complete legion to c.1200.
Nathan Ross
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