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How did Rome physically attempt to defend the Eastern Frontier from 226 to 363

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How did Rome physically attempt to defend the Eastern Frontier from 226 to 363?

In providing an answer to how Rome physically protected the Eastern empire between 226AD and 363 AD this essay will first describe the broad changes in defensive strategy that Rome enacted in response to attacks by its enemies.  The key drivers of these changes will be detailed along with the key personalities that drove those changes and what effect they had.  Changes to the structure and the changes to the physical makeup of static defences will be discussed along with an examination of the key points of the debate that surrounds the concept of defence in depth.

At the beginning of the third century a new strategy was developed and employed by Rome’s military leadership. Beginning with Hadrian, the revamped Roman military structure was downsized in an attempt to develop a more low cost and low drag military structure. The large central reserve of troops had become economically unviable and the tooth to tail ratio, or the ratio of combat troops to logistical support troops had become unmanageable. As this central reserve was downsized the most obvious strategic issue that came to the forefront was that danger to Rome should the perimeter collapse.  To combat this problem a defensive strategy was developed that rested on a networked transport solution of interconnected roads and rivers by which special military units could be transported to provide reinforcements.[1] Over the course of the third and forth centuries, the Romans became increasingly aware of the danger posed by the highly mobile tactics employed by their enemies. In response to this they became an overhaul of their static defensive lines, forts and other compound fortifications. This overhaul was designed to defeat the Persian cavalry by placing higher fortification in the line of advancing invaders.  

Military command structures, ancient or otherwise, are reticent to alter strategies unless there is an overwhelming reason to do so. The large, networked US military suffered a series of setbacks by a small, agile, asymmetric and highly adaptable insurgency in both Iraq and Afghanistan. The result, a complete overhaul of military doctrine and the initiation of a new counter insurgency based doctrine actress the entire US military apparatus. For the Romans defending the Eastern Empire, a similar decision making process was undertaken, and for similar reasons. The key driver for change was the series of humiliating defeats inflicted on the Romans by the Sassanian Persians and the Parthians. As a result of these defeats Roman military leaders sought to impede their enemy’s most effective tactics. The Romans had seen just how effective the Persian cavalry could be. The defeat of Roman emperor Gordian III by Sharpur was recorded with the chilling words, “Gordian Caesar was killed and the Roman force was destroyed”. [2] Resultantly the Romans sought out a strategy that they hoped would impede the rapid deployment and movement of their agile enemies.

This changes in strategy occurred, in the main part, under the direction of Diocletian (AD284 – AD305), Cameron describing this time period as a, “phase of recovery, consolidation and major social and administrative change”.[3] Determined to restore Rome to a stable footing, Diocletian began by decentralising the power base of the roman elite by forming a tetrarchy.[4] Initially he established a Diarchy with himself based in East to defend against the Sassanians and Maximilian based in the west. To this Diocletian added two more, and established the tetrarchy, with Galerious and Constantius with responsibility for the Balkans and the Germany respectively.[5] According to Luttwack, Diocletian also sought to provide the military with additional resources, in effect turning the entire empire into a “regimented logistical base” [6]. He reintroduced conscription, leading to a significant increase in the size of the Roman military. He also initiated a massive works program aimed at upgrading the static defensive structures of the Roman front, as well as building new military grade roads for the rapid movement of troops. This integrated system is evidenced by the archaeological remains that populate the areas between Palmyra and Azarq.[7] Archaeological evidence also leads to the conclusion that Diocletian’s endeavours were favourably viewed, an inscription from Palmya detailsl the response to Diocletian’s attempts to strengthen the empire against its enemies,

‘Restorers of the world of whom they are the masters, and leaders of the human race, our lords Diocletian (and  Maximianus), unconquered Emperors, and Constantine and Maximianus, noblest Caesars, have established this entrenchment under favourable auspices.’[8]

Across Rome’s Eastern frontier old forts were reinforced made into stronger static defences. Archaeologists are unable to date many of the remains but believe that the addition of towers signals works enacted under Constantine.  High towers found by archaeologists are believed to have been utilised as signal posts to communicate with other forts along the line of defence.  Experiments conducted by archaeologists in Lejjun area showed that signal flares could be seen by the forts at Khirbetel-Fityan, which in turn could send signals to Lejjun fortification. These forts were used by the Roman’s as, ‘bases for patrols, local administrative centres, watering places, stopovers for travellers and couriers, and guard posts along the routes of communication.’[9] Archaeological digs have shown that a number of older forts were upgraded to a higher defensive specification. The earlier layout of twin parallel ditchers was modified by joining the ditch. Towers were added and gates were significantly improved by constructing a large bastion and walls were strengthened by doubling the thickness. These older but upgraded forts are usually larger than the newer forts constructed in between them. [10]

The physical defence of the empire has two components, the static defences and the men who were stationed at those defence points.  The same key drivers, defence against a highly mobile enemy saw the changes in how manpower and unit disposition played a part in the physical defence of the empire continue under Constantine. He enacted a number of unit based changes that saw the expansion of the camitatus[11]into much larger regional field armies which were withdrawn from the frontiers and the border lines. He made changes to the makeup and disposition the cavalry, mobilised a new infantry unit called the auxilia[12] and moved the older established units based on the frontier and replace them with newer units. [13]  The changes wrought by Constantine have been criticised as a ruination of the good work done by Diocletian. Zosimus in particular has little positive to say about the changes made by Constantine,

‘By the foresight of Diocletian, the frontiers of the Roman empire were everywhere studded with cities and forts and towers...and the whole army was stationed along them, so it was impossible for the barbarians to break through...But Constantine ruined this defensive system by withdrawing the majority of the troops from the frontiers and stationing them in cities which did not require protection.’[14]

Successful or not, changes were made and not simply in terms of the formation of unit and the methodology of building static defensive lines. Strategy, grand or not, was changing from a system of system of buffer client states and mobile troops in the first century AD, to a defensive cordon of stationary troops in fortifications on the frontier in the second and third centuries. Moving beyond that we see the establishment of the strategy of ‘defence in depth’, a strategy that saw the deployment of cavalry units and permanent garrisons both in front of and behind the main border line of the empire.[15] Garrison troops of reduced stature manned static defences wheel field armies of smaller more mobile and flexible units were held in reserve ready to bolster defences.[16] The theory of defence in depth has its most vocal supporter in Edward Luttwak, who posited that defence in depth was the acceptance by military leaders that the frontier provinces would themselves be the main combat zones in operations against Rome’s enemies. Luttwak’s main assertion was that the grand strategy of the Romans, “was to provide security for the civilization without prejudicing the vitality of its economic base and without compromising the stability of an evolving political order.”[17] This marked a change from the idea that the lands belonging to the enemy’s would be the main arena for combat, an idea that saw acceptance of the fact that Rome’s borders would come under constant harassment. This change in strategy may not have been a conscious design, rather Luttwak argues that while the Romans did not conceive of ‘grand strategy’ explicitly they,  “nevertheless designed and built large and complex security systems that successfully integrated troop deployments, fixed defences, road networks, and signalling links in a coherent whole.” [18]

Defence in depth was modelled on the idea that defensive troops would not directly engage attacking forces, but would rather drawback to fortified positions of strength and wait for mobile cavalry to engage the enemy. The most significant issues with defence in depth are the trade off between weaker frontier units for stronger fortifications.. The defence in depth strategy, while it may have had a destabilising effect on Rome and its civilisation did retain greater flexibility in the face of the new threats that Rome faced. These new high intensity threats, from multiple sources required a significant change in strategy and defence in depth provided that by providing a greater economy of forces that increased the presence of Roman troops all along the border line. [19] Luttwaks theory rests, according to Keegan, on six assumptions. These assumptions underlie Luttwak’s analysis. Keegan determined that Luttwak’s first two assumptions pertain to the goals of the Roman Empire, the nest two to its frontiers, and the last two to the unitary quality of the system of defence.[20]  Looking at Luttwak’s first assumption Keegan notes that that he assumed that the Roman legionary deployment and the fortification that they manned met defensive not offensive objectives. Secondly there is the assumption that the Roman Empire expanded in order to achieve a defensible frontier. Beyond that there is the third assumption that the purposes of each of the fortifications can be deduced purely from archaeological examination. Frothy these frontiers were established and therefore fixed and identifiable. Fifthy there is the assumption n that the Romans had developed a single cogent system of defence that was uniform across the empire regardless of leadership, terrain, objective, and currant poetical climate. Lastly Luttwak assumed that the phases of this grand strategy evolved in a natural linier order from one state to the next.[21]

Luttwak’s theory is disputed by Issac who believed that as the empire did not have a general staff to sustain grand strategy of defence they instead relied on an aggressive mindset and operation tempo through that traded defence for offence right up until the fourth century.  This dispute is by no means limited to Issac, with Keegan providing a detailed analysis of the assumptions listed above. Firstly the idea that the goal of the grand strategy was to provide a pure defensive line disputed by Issac on the grounds that his examination of the Talmud shows that there principle purpose was internal enforcement. Keegan quotes from the “The Frontier Policy of Septimius Severus: New Evidence from Arabia,” to show that there are inscriptions throughout the Eastern empire that show that the role of the legions was internal security. [22] Looking at the functions of the fortifications Keegan notes that it is not possible to directly  discern, as Luttwak has do, that the role of a particular fort is identifiable from its remains, let alone to entire system of fornication, So there is no real way to tell the purpose of the entire line of Eastern fortifications.[23] Examining the idea that the system was unitary Keegan notes that no real system of defence in depth was employed in the 250’s Ad during the Roman response to the attacks by the Persians. [24]

These criticisms of Luttwak by Keegan reflect the early work that Luttwak performed and the fact that historical evidence, when presented for the first time, and in a strong manner, as Luttwak’s premise was delivered, have a tendency to assume a pivotal and unassailable role in the narrative of historical analysis. That Luttwak performed a valuable service is not in dispute, but a modern reading, in far more detail that this paper allows for, can easily ascertain that there are significant holes based on the assumptions that he made.

The Romans’ used the perimeter defence against Shapur which lead to the  loss of three emperors to him, Gordian III, Phillip the Arab and lastly Valerian who was captured by Shapur and his fearsome Sasanian knights, the Savaran. What followed for the Roman Empire was a time of turmoil, emperors came and went and usurpers tried to wrench control of the empire for themselves rather than concentrating on trying to upgrade the troops in order to protect not only the Provinces but also the borders of their empire that is until late third century. Changes in defensive posture did help keep the empire intact and Romans safe. However in the long term these changes were not enough to fully protect the Eastern Empire from the inexorable approach of their enemies.  


Primary Sources: Works Cited

Ammianus M(1986)The Later Roman Empire (AD 354-378) - London : Penguin Books.

Zosimus , (5th century )Historia Nova.

Secondary Sources: Works Cited

Bishop M.C & Coulston J.C.N(2006)Roman Military Equipment from the Punic Wars to the Fall of Rome 2nd Ed - UK : Oxbow Books limited.

Butcher K(2003)Roman Syria and the Near East - London : British Museum Press.

Cameron A(1993)The Later Roman Empire - Oxford : Fontana Press.

Dodgeon M & Lieu, S(1991 Repr1994)The Roman Eastern Frontier and the Persian Wars - London : Routledge.

Elton H(1996)Warfare in Roman Europe AD 350-425 - Oxford : Oxford University Press.

Goldsworthy A (2003)Complete Roman Army - UK : Thames and Hudson.

Goldsworthy A (2000)Roman Warfare - UK : Cassell: Wellington House.

Isaac B(1990)The Limits of the Empire, The Roman Army in the East - Oxford : Oxford University Press.

Keegan K, (2006) “ Redefining Roman Grand Strategy” ,  The Journal of Military History, 70:2

Jones A.H.M(1964)Later Roman Empire - U.S.A : University of Oklahoma Press.

Luttwak E(1976)The Grand Strategy of the Roman Empire - London : Widenfeld and Nicholson.

Thompson G (1979)Die Oracula Sibyllina - New York : Arno Press.

Tomlin R.S.O & Wacher,J (Ed)(1987)The Army of the Late Empire in the Roman World - London : [s.n.]

Other Refrences:

  Freeman, P & Kennedy, D (ed)(1986). ‘The Defence of the Roman and Byzantine East’: British Archaeological Reports, S297, 2 vols: Oxford

Kennedy, D & Riley, D (1990)‘Rome's Desert Frontier from the Air’: Batsford Limited, London

Lee, A.D (1993) ‘Information and Frontiers, Roman foreign relations in late antiquity’: Cambridge University Press, Cambridge

Oates, D (1968) ‘Studies in the Ancient History of Northern Iraq’: British Academy, Oxford

Whittaker, C.R (1994): ‘Frontiers of the Roman Empire-A Social and Economic History’ : Johns Hopkins University Press, Baltimore


[1] Butcher, K (2003) : ‘Roman Syria and the Near East’: p415

[2] R.N. Frye, (1984(The History of Ancient Iran pp 371-3 in F Millar, (1988), Government and Diplomacy in the Roman Empire During the First Three Centuries, The International History Review, 10:3, 346

[3] Cameron, A (1993) : ‘The Later Roman Empire’:p30

[4] Cameron, A (1993) : ‘The Later Roman Empire’: p31

[5] Ralph W Mathisen, (1997) Diocletian, “ De Imperatoribus Romanis” University of South Carolina,  http://www.roman-emperors.org/dioclet.htm accessed 15/01/11

[6] Luttwak, E (1976) : ‘Grand Strategy of the Roman Empire’: p177

[7] Butcher, K (2003) : ‘Roman Syria and the Near East’: p416

[8] Dodgeon, M & Lieu, S (1991 Repr 1994) ‘The Roman Eastern Frontier and the Persian Wars’: 5.5.5 p136

[9] Butcher, K (2003) : ‘Roman Syria and the Near East’: p419

[10] Elton, H (1996): ‘Warfare in Roman Europe AD 350-425’ p151-152

[11] A small central field army: MacDowall, S and Hook, C, (1995) Late Roman Cavalryman 236-565AD: p4

[12] A small infantry field unit with the strength of 500 men: MacDowall, S and Hook, C, (1995) Late Roman Cavalryman 236-565AD: p4

[13] Jones, A.H. (1964): ‘Later Roman Empire’: p608

[14] Zosimus (5th century) : ‘Historia Nova’: XI.54.5

[15] Butcher, K (2003) : ‘Roman Syria and the Near East’: p405

[16] Penrose, J, (2008) Rome and her Enemies, an Empire Created and Destroyed by War :p243

[17] Luttwak, E, (1976), Grand Strategy of the Roman Empire from the First Century A.D. to the Third,  1

[18] Ibid 3

[19] Keegan, K (2006), Redefining Roman Grand Strategy, 338

[20] Ibid 337 - 340

[21] Ibid

[22] Ibid, 339

[23] Ibid, 342

[24] Ibid, 345

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