|It's all in the
The strength of Late
Roman armies and units
By Robert Vermaat
A question often heard
is how the armies and units of the late Roman army
compare to those of the Roman armies of the Republic and
the Principate. This article provides a short discussion
of the numbers provided by the sources.
The Late Roman
First of all, how large
was the Late Roman army anyway? The Notitia Dignitatum ,
written in c. 394 AD and updated over the next two
decades, actually lists the following units for both
parts of the Empire:
12 scholae palatinae,
146 field army legions or legiones comitatenses,
42 border legions or legiones limitanei,
97 auxilia palatinae,
85 field army vexillations,
196 cohortes, auxilia and milites,
253 border units of cavalry (ale, cunei equitum and
I will discuss the
actual unit strength below, but if we assume that, on
average, the scholae numbered 500 per unit,
field army legions 1.000, border legions 3.000, auxilia
palatina 800, border infantry units 300 and cavalry
units 350, the total of units mentioned in the Notitia
Dignitatum yields an army of about 450.000 men.
However, scholars such as Nicasie think this might be
seen as a minimum rather than a maximum, to be taken as a
more realistic number, as opposed to a 'paper strength'.
The establishment strength could even be 650.000 if each
cohort indeed was to be 500, and this number is what
Agathius gives us for the 4th-c. army: 645.000 (Agath. V.13).
Of course, it could well be argued that since each unit
may have been understrength at many times during their
existance, the lower number would probably be a good
Was there a 'typical'
Roman army? Did Roman generals have an 'ideal' number in
mind, depending on circumstances such as the season or
logistics? Vegetius, talking about what he believe was
practise during the Principate, thought 24.000 was the
maximum for a field army in a large campaign (Veg Epit
Maurice/Maurikios thought a field army of 36.000 (24.000
infantry and 12.000 cavalry) was the upper limit for
campaigns, and 5.000 to 15.000 average forces (Maur Strat
II.4.28-33, III.8.31-40 and III.10-16-28. he clearly
regarded 12.000 cavalry as many (XII.B.13.5-7, XII.B.8.33-36,
Of course, such theories
could differ from reality. A few examples:
- A field force of 38.000
is reported in the Balkans in 478 AD (Malchus fr.
18.2.12-23), being two forces combined: one of
the regional armies under the magister
militum per Thracias comprised of 10.000
infantry and 2.000 cavalry, while the other
praesantal army comprised of 20.000 infantry and
- In early 503 AD, a
field force of 52.000 strong was created
combining two armies of roughly 20.000 each under
the two magistri militum preasentalis
with 12.000 troops of the magister militum
per Orientem. This number did not include
either local limitanei units or Arab
federates. Procopius assumed this was the largest
Roman field army ever (Proc. Bella II.24.12-17).
That he was quite mistaken can be seen in the
- Belisarius fielded
30.000 men at Dara, 530 AD (Proc Bella I.13.23),
20.000 men at Callinicum, 531 AD (Proc Bella I.18.5-7)
and over 17.000 men in Africa, 533 AD, of which 5.000
cavalry and 10.000 infantry (Proc Bella III.11.11).
Roman Armies on campaign :
188.000 - army of Maxentius, 312 AD (Zosimus II.15.2)
165.000 - army of Licinius, 324 AD (Zosimus II.22.1)
130.000 - army of Constantine, 324 AD (Zosimus II.15.2)
130.000 - army of Licinius at Chrysopolis, 324 (Zosimus
100.000 - army sent to Africa 457 AD (Procopius Bella III.6.1)
98.000 - army of Constantine, 312 AD (Zosimus II.15.1)
70.000 - army of the rebel Gildo, 398 AD (Orosius VII.36.12)
65.000 - main Roman army in Persia, 363 AD (Zosimus III.13.1)
50.000 - garrison of Egypt, 269 AD (Zosimus I.44.1)
35.000 - army of Licinius at Cibalae, 317/8 AD (An. Val.
30.000 - army of Macrianus, 261 AD (SHA, Gall. Duo II.4)
30.000 - army of the magister peditum Barbatio, 357 AD (Lib.
Or. 18.49), Ammianus has it at 25.000 (AM XVI.11.2)
30.000 - army of Procopius, Persia 363 AD (AM XXIII.3.5)
30.000 - Roman army in Armenia, 543 AD (Proc. Bella II.24.16)
25.000 - army of Galerius in Persia, 298 AD (Festus Brev.
23.000 - army of Julian, 360 AD (Zosimus III.10.2)
20.000 - army of Constantine at Cibalae, 317/8 AD (An.
20.000 - army of Vetriano, 350 AD (Jul. Or. 2.77B)
20.000 - army of Procopius, Persia 363 AD (Lib. Or. 18.214)
though Zosimus has it at 18.000 (Zosimus III.12.5) and
Malalas at 16.000 (Chron. XIII.21)
20.000 - Roman army in Mesopotamia, 531 AD (Proc. Bella I.18.5)
15.000 - Roman army in Africa, 533 AD (Proc. Bella III.11.2)
15.000 - Roman army in Illyria, 548 AD (Proc. Bella VII.29.3)
As referred to above, a
lot can depend on what we determine was the actual unit
strength for each Late Roman unit. Nicasie estimates the
following Late Roman unit strengths:
- scholae -
- legiones (comitatenses)
- legiones (limitanei)
- auxilia palatinae -
- infantry units (limitanei)
- cavalry units (limitanei)
The traditional legion had been 6000 strong. Johannes
Lydus also mentions this high number (De Mag. I.46).
Vegetius mentions two very strong legions of 6000, but he
stresses that legions 'in his day, although the name
legion still existed, were much smaller in size.' (I.17,
II.3). Vegetius' 'old legion' numbered 10 cohorts, the
first numbering 1105 infantry and 132 cavalry, the others
555 and 66, totalling 6100 infantry and 726 cavalry (II.6).
However, it is generally assumed that if this
organisation ever existed, it probably belonged to the
early 3rd century.
It was Mommsen who first noticed that old style legions
were probably broken up into 6 detachments of a 1000,
each of these commanded by one of the 6 tribunes of the
old unit. Only the legions of the limitanei were
still commanded by praefecti. Only Nischer
proposed that 'new' legions existed of two units of 500,
drawn from every border legion, but his theory lacks
evidence. However, the Beatty papyrus mentions
detachments of 500 men. One vexillatio consisted of 1000
men from legio III Gallica and legio I
Illyrica. Another, from legio II Traiana,
consisted of two 500-men units. Two vexillationes
of legio III Diocletiana numbered 1100.
Border legions seems to be much larger than field army
legions, because they are usually divided over as much as
When in 359 AD 7 legions (including equites indigenae,
two units of superventores, praeventores
and comites sagittarii) were trapped at Amida,
they numbered 20-25000 men together with the inhabitants
and refugees (XIX.2.14). Two of these legions suffered
400 casualties during a sortie (XIX.6.11). If we assume
there were 7500 civilians, this hardly allows for more
than 1500 per legion, if the garrison was not a legion of
6000 or if there weren't even more civilians than assumed.
All in all, it seems that Late Imperial legions numbered
between 1000 and 1200.
During the time of Septimus Severus, a reorganisation
apparently resulted in cohorts 550 strong (up from 480),
possibly those meant by Vegetius (II.6). But see below.
Ammianus mentions that Julian sent detachments of 300 men
from each unit to Constantine (XX.4.2). In 378, Gratian
sent detachments of 500 men to storm the position of the
Lentienses (XXXI.10.13). Also in 378, Valens sent
detachments of 300 from each legion to meet the Goths at
It is thought that some of these detachments never
returned to their parent unit but retained the original
name (hence the repetition of such names in the Notitia
Dignitatum lists). It is also possible that many of the
field army units were split up into iuniores and
seniores, reducing the original strength of
these units. But another view on this is that the iuniores
were a cadre of the original (hencefort designated as seniores)
unit, which was therefore doubled in the process.
Infantry units mentioned by Ammianus number 300, 500, 800,
1000 and 1500 (XVII.1.4, XVIII.2.11, XXIV.1.6, XIV.1.2,
XXIV.6.4, XXV.6.13-15, XXV.7.3).
Johannes Lydus mentioned cohortes of 300 and vexillationes
of 500 (De Mag. I.46).
The old style alae numbered 500 and seem to have
remained that way. On paper at least. On the basis on the
Beatty papyri, Duncan Jones calculated that around 300 AD
in the Thebaid (Egypt), a unit of equites was
121 strong, an ala 116 and a cohors 164.
These may not have been complete units, or else very much
Nothing much else is known about cavalry unit strengths.
The ala III Assyriorum was organized in old-style
11 turmae, giving it a possible strength of 350
(ChLA XVIII 660). Ammianus mentions that the cataphracti
defeated at Strasbourg were 600 strong, which is echoed
by Johannes Lydus who says that alae were that
number, and turmae 300 but also 500 (De Mag. I.46).
Ammianus also mentions two turmae at Amida
numbering 700 together (XVIII.8.2). Procopius has various
sizes, between 200 and 800 strong (800: Bella VI.5.1, VI.7.25-6).
Some units are larger, between 1000 and 1500, but it is
unclear if these are units grouped together, or maybe
allied forces (1500: Bella V.27.22-3 and VII.34.42).
Maurikios mentions cavalry units should be between 300
and 400, but in any case not less than 200 and not above
400; if understrength, they should be combined.
Finally, the Anglo-Saxon Chronicle mentions that in a
battle in 457 AD, '4 units' of Britons were destroyed,
while another version of the text mentions a number of
4000. (ASC. Laud Chronicle year 456, Parker Chronicle
Two main conclusions can
be drawn of Late Roman units (Nicasie):
a) in practise, the actual number of troops fielded will
have been lower than the paper strengths.
b) it seems possible that Late Roman units did not have
fixed establishment strengths at all, but varied between
a certain minimum and maximum according to need.
Marcellinus: With an English translation, ed. and
trans. J.C. Rolfe, 3 vols., (Loeb Classical
Library, London/Cambridge 1935, repr. 1971-2).
Marcellinus: Res Gestae Divi Augustae, full text
- Notitia Dignitatum,
IN PARTIBUS OCCIDENTIS, IN PARTIBUS ORIENTIS, full text (Latin) at: http://www.gmu.edu/departments/fld/CLASSICS/notitia.html.
- Notitia Dignitatum,
full text (English) at: http://www.fordham.edu/halsall/source/notitiadignitatum.html.
- Procopius of
Caesarea: History of the Wars, trans. H.B. Dewing,
full text (English) at: http://bulfinch.englishatheist.org/Procopius/index.htm.
- Zosimus': Historia
Nova, tr. unknown (1814), ed. Roger Pearse, in:
Early Church Fathers - Additional Texts, at: http://www.ccel.org/p/pearse/morefathers/home.html (scroll down to page
bottom for Zosimus).
- Hoffmann, Dietrich
(1969): Das Spätrömische Bewegungsheer und die
Notitia Dignitatum, 2 vols., Epigraphische
Studien 1, (Rheinisches Landesmuseum Bonn).
- Nicasie, Martijn (1997):
Twilight of Empire, the Roman Army from the Reign
of Diocletian until the Battle of Adrianople, (Thesis