Category Archives: Ancient History

How did the Romans respond to the threat posed by Sassanian Persia and how effective was that response?

This is the first in my series of undergraduate essays, which I’ll be putting up once a week (on Saturdays).

I will be putting them up in chronological order of the subjects considered, with each essay being followed by a complete bibliography of the texts cited, and then the general feedback provided by my tutors.

This essay was given a high 2:1 in my first year at university.

How did the Romans respond to the threat posed by Sassanian Persia and how effective was that response?

The threat of Sassanian Persia was unlike anything the Roman Empire had faced since the Punic Wars, with a few of their leaders being comparable to Hannibal in terms of their skills as military leaders. The offensive capability of the Sassanian armies initially stunned Roman generals; their much improved mobilisation by comparison to their Parthian predecessors, combined with their skilled use of siege warfare was a fearsome combination[1]. As well as this, the Sassanians made great advances in the building of fortifications[2], which were to have a significant impact on the value of the various Roman responses through the period.

The response from the Roman Empire to this new and challenging threat was almost exclusively based in the military, and in foreign policy. The Roman military response can be divided into the actual campaigns and raids undertaken across roughly four centuries, and the instigation of various reforms which included the make-up and organisation of the Roman forces in the area, and the definition of the frontier. Alongside and frequently resulting from this, there was the more diplomatic side, which included the assorted peace settlements. The latter was distinctly in the minority in terms of the overall Roman response. The response to the danger presented by the nascent Sassanian Empire had differing levels of success, ranging from successful campaigns such as that of Carus in AD 283, who invaded Mesopotamia and reached and captured Ctesiphon (the capital)[3], to the resounding failures which included that of the first invasion by Severus Alexander in the early 230s[4], as well as the countless successful raids made by Sassanian forces into Syria.

As previously stated, the Roman response was overwhelmingly military in nature, and consisted of an assortment of raids and campaigns into Sassanian territory of varying strength and success, as well as the perhaps more subtle changes in organisation of the frontier fortifications, and the forces stationed there. The initial Roman military response was led (as mentioned prior) by Severus Alexander in the 230s: a campaign which aimed at capturing a greater portion of Armenia, but was resoundingly unsuccessful[5]. Following this, there were further planned invasions by Gordian in 244, Valerian in 260, Aurelian in 275, Carus in 283, Julian in 363 and finally much later by Heraclius in 626. These campaigns almost exclusively failed, for a range of reasons. Gordian was killed, “by the treachery of Philip who reigned after him,”[6] Valerian was defeated or tricked and captured or killed, depending on which source is read.[7] Aurelian was assassinated before setting off, and Carus was to a certain extent successful but was ultimately killed during a thunder storm in Ctesiphon, following which his superstitious troops fell back.[8] Julian’s expedition looked promising until he realised that he was unable to take the heavily fortified Sassanian cities, including Ctesiphon, despite his veteran army of 60,000. This fact turned his invasion into a mere raid, however large, and he turned back for Roman territories and was harried by the more mobile Sassanian army, eventually leading to his mortal wounding and death.[9]

The Roman Empire also made internal changes in response to the danger of the Sassanian Empire. The vast majority of these were made up by reforms, both in the distribution and make-up of Roman forces, and how well the frontier was defined (particularly by the construction of fortifications). There are various historiographical debates, most of which are addressed by Isaac[10] surrounding how much the various sources and archaeological evidence should be interpreted by modern historians.

One of the more useful sources for determining the organisation of the late Roman army is the Notitia Dignitatum; a late fourth century document showing the disposition and location of units. The Notitia Dignitatum shows that there were increasing numbers of cavalry units, including the emergence of equites sagitarii or horse archers, and heavy cavalry (clibanarii or cataphractarii) on the eastern frontier.[11] These types of troops were very similar to those used by the Sassanians, the worth of which had been proven time and again when used against the Romans. It was only natural therefore that the Romans, being a very pragmatic military force would adopt successful troops and tactics as their own.

As well as the new expanded use of cavalry, there began to be a differentiation between limitanei or border guards[12]  and comitatenses or soldiers of the field armies. It is suggested that this distinction began to be made from the reign of Diocletian, but it was more widespread by 325 C.E., under Constantine.[13]  As Isaac addresses however, there are limitations to the Notitia Dignitatum in that it was a bureaucratic list, and so did not provide anything but information, about the formal structure of the army (rather than the reality). Even that was fairly vague; it gave the disposition of units at undefined dates[14] which obviously meant that it is of limited accuracy. The thought was that the limitanei would defend the borders only, while the field army would move around to reinforce, or to launch raids and campaigns into Sassanian territory.

The reforms were not restricted to just the army however: increasingly different and improved fortifications emerged on the eastern frontier during the Diocletian period. The exact nature and purpose of these fortifications is debated although according to a contemporary source, Diocletian built a series of forts in the frontier regions between Egypt and Persia.[15] This series of forts could be argued to be part of the strata Diocletiana, a view which is supported by Van Berchem[16], and this coupled with the presence of a second fortified road running parallel to it arguably provides evidence of an increasing emphasis on the security of northern Syria, as a direct response to Sassanian aggression. The function of the new fortifications is debated, with Luttwak in particular making a case for the forts being used in merely a defensive capacity, as part of his ‘defence in depth’ theory,[17] conjecture which has become popular among historians. By contrast, Isaac dismisses it, pointing out that in no contemporary sources is there any evidence for a Roman strategy of ‘defence in depth,’ and that it would be incorrect to deduce too much.[18] As well smaller and separate fortifications, there was a definite improvement in the fortifications of cities under Diocletian, and this was to play a pivotal role in the Roman response to Sassanian invasions, as shall be addressed later on.

Politics also played a significant part in the overall Roman response showing it was not necessarily limited to simply military action. Initially, the Romans made the misjudgement to support the outgoing dynasty, offering the Arsacids refuge, and supporting the Arsacid king of Armenia which resulted in gaining the city of Hatra as a protectorate. This would seem only to provoke the newly established Sassasnian leadership.[19]There were despite this, periods of peace between the Roman and Sassanian Empires, and the various treaties were usually designed to be lasting. Perhaps the most notable of these resulted when Narses of Persia invaded Armenia and was thrown back by Diocletian. The peace settlement which followed compelled Persia to cede no fewer than five provinces beyond the River Tigris (the previous border). These provinces were intended (much like the conquered section of northern Mesopotamia) to be a ‘buffer’ zone against Sassanian aggression, but were lost soon after, following Julian’s disastrous campaign in 363.[20] Other settlements included the peace of Nisibis in 297, and a peace made by Kobad in the mid-fifth century. Noshirwan also made numerous peace settlements, the first of which was in 531 involving Rome paying eleven thousand pounds of gold, and the second following his later capture of Antioch, which again involved Rome paying war indemnities to the Sassanians.[21] These would seem to show that as Rome became increasingly aware it would not be able to subdue the Sassanian Empire, they became content with simply paying it off.

How successful the Roman response was is very open to interpretation. It is possible to argue that due to the fact that the Roman Empire survived past the end of its Sassanian counterpart (at least in the form of the Byzantine Empire), the measures put in place were effective. Such a view however is too simplistic, as the Roman Empire did not arguably suffer anywhere near the same external pressures in the east as the Sassanian Empire. The main reason for the fall of the Sassanian Empire was arguably the emergence and rapid spread of Islam[22], and while the Roman Empire did fragment under the pressure of the ‘barbarian’ migrations, the Byzantine Empire emerged as its recognisable incarnation. A perhaps more plausible argument for the success of Rome in dealing with the Sassanian Empire is that, although there were some very successful raids into Roman Syria and Mesopotamia, very little land was actually lost control of, with the exception of the five provinces lost in 363. The main reason for this was the improvement and expansion of the fortifications present in the area, and protecting the various cities – a result mainly of the reforms of Diocletian, and aided by Constantine’s later additions. As well as this, there were some successes on the offensive, however few. Most notably were those of Carus in 283 when he reached the Sassanian capital of Ctesiphon, and Diocletian in 296-8 who ceded five provinces from Persia as a result of a resounding victiory[23].

Despite these viewpoints, it seems overwhelmingly clear that taken individually, the Roman responses to the immediate threats of various Sassanian monarchs was woefully inadequate. This manifested throughout both the Roman offensive and defensive operations in the area. The fact that the vast majority of the various campaigns into Persia were ineffective at best, and damaging to the Roman Empire at worst clearly showed that in this respect the response was if anything, counter-productive. One end of this spectrum can be demonstrated by the planned campaign of Aurelian in 275 which never went ahead and so achieved nothing, with the other extremity (of which the examples are far more numerous) being embodied by Severus Alexander’s initial invasion in the early 230s, as well Gordian’s failed advance of 244,[24] and Julian’s later campaign in 363.

More generally, it was the increasing Roman inability to hold ground, traditionally achieved by taking towns and cities, which meant that their invasions were largely ineffective. When coupled with their obscure strategic aims, this would seem to dismiss any the potential impact of a Roman response to Sassanian aggression. The inability to capture the newly fortified settlements on both sides of the frontier meant that any military action was reduced to mere raiding, no matter on what scale. The raiding style of warfare was not necessarily suited the Roman army, whose core was made up of the heavy infantry of the legionnaires, despite the increasing amount of cavalry in their field army. By contrast, the Sassanian army maintained the traditional strong units of both light and heavy cavalry which had been inherent to the Parthian armies. This contrast meant that any incursion into Persia would have been harried by light cavalry, and as soon as the Romans decided to retreat (following the realisation that they were unable to take any meaningful territory), they would be easily caught by the far more mobile Sassanian forces, as is shown most poignantly by Julian’s retreat in 363.[25] The difference in mobility also meant that Sassanian armies were capable of taking the initiative against the seemingly ponderous Roman legions, and were more than capable of destroying superior forces.[26]

In defense, the Roman Empire was also found somewhat lacking for, while they did not really lose any significant territories for any length of time, they were incapable of dealing with the large scale Sassanian raids. Similar in nature to the Roman campaigns, there were a few very significant differences. Primarily, as already mentioned, the Sassanian armies were generally far more suited to raiding than their Roman counterparts, but also importantly, the campaign aims of the likes of Shapur I and II in particular was not to take ground at all, it was to plunder and raid, and so they were prepared for a particular style of warfare, which their Roman equivalents were not. The Roman defence system was also arguably non-existent. Although there were undeniably troops positioned to defend against small-scale, nomad raids, it is debatable whether or not there was in fact a true system for defending the frontier in place.[27] Past the improved fortifications commissioned by Diocletian at the end of the third century, the individual populations of towns and cities were generally responsible for their own defence, and any attempt at defending the hinterlands surrounding settlements was abandoned as impractical.[28] Many of these measures were arguably ineffective against the larger-scale and fairly common raids of the Sassanian army, which consistently managed to penetrate as far as Syria, and involved the occasional capture of cities, such as Antioch[29] (on the Mediterannean).

It is fair to say that the Roman response to the danger posed by the emergent Sassanian Empire was overwhelmingly military in its nature, due to the fact that it consisted almost exclusively of military campaigns, with the peace settlements usually being the results. The internal reforms too, were focused solely on the military, with the distribution of troops and the advances and construction of fortifications. While the value of the primary sources is questioned, and the function of the new fortifications is debated,[30] it is undeniable that the measures were taken in response to the Sassasnians, due to the fact that the campaigns were into Sassanian territory and also that the various construction works and reorganisations were undertaken in the reigns of Diocletian and Constantine – at a time when the only major threat in the east was the Sassanian Empire. Aside from the occasional successes in the field, the responses of the Roman Empire were largely unsuccessful, as the rivalry last for closing on four centuries, with no decisive victory for either side. The Romans did not have any lasting victories on the offensive, apart from under Diocletian, and on the defensive, despite the expansion of fortifications, and the reorganisation of the army the Sassanians were seemingly able to raid at will into Roman territory. In short, the Romans formed a military response, although it only gradually became clearer in its aims, as they massively misjudged the calibre of their opponents, and so perhaps treated them with undue contempt for far too long.[31] This inhibited the effectiveness of the response for so long that it eventually did not make much of a difference. There are obviously reasons for the seeming lack of interest in the eastern Empire, particularly later on, with the barbarian migrations resulting from the movement of nomads out of the Steppes into eastern Europe. These migrations posed an arguably much more serious threat to the stability of the Empire, and they are sometimes given as the reason for the fall of Rome.

Word count: 2,901

[1] D.S. Potter, ‘The Transformation of the Empire: 235-337 C.E.,’ in ed. D.S. Potter, A Companion to the Roman Empire, p.157-8

[2] P. Sykes, A History of Persia, p.35

[3] P. Sykes, A History of Persia: Volume 1, pp.407-8

[4] D.S. Potter, ‘The Transformation of the Empire: 235-337 C.E.,’ p.158

[5] For a full contemporary account, see Herodian VI, 5, 1-6, 6 in M.H. Dodgeon and S.M.C. Lieu (eds.) The Roman Eastern Frontier and the Persian Wars (AD 226-363), pp.23-6

[6] Eutropius, breviarium IX, 2, 2-3, 1 in M.H. Dodgeon and S.M.C. Lieu (eds.) The Roman Eastern Frontier and the Persian Wars (AD 226-363), pp.36-7

[7] M.H. Dodgeon and S.M.C. Lieu (eds.) The Roman Eastern Frontier and the Persian Wars (AD 226-363), pp.59-62

[8] P. Sykes, A History of Persia, p.33

[9] P. Sykes, A History of Persia: Volume 1, pp.418-22

[10] B. Isaac , The Limits of the Empire: The Roman Army in the East

[11] N. Pollard, ‘The Roman Army,’ in ed. D.S. Potter, A Companion to the Roman Empire, p.226

[12] For a fuller description, see B. Isaac, The Limits of the Empire, pp.208-13

[13] N. Pollard, ‘The Roman Army,’ p.226

[14] B. Isaac, The Limits of the Empire, p.161-2

[15] Malalas, XII, pp.308, 17-22, Ammianus Marcellinus XXIII, 5, 2, and  Procopius, de bello Persico II, 5, 2-3, in M.H. Dodgeon and S.M.C. Lieu (eds.) The Roman Eastern Frontier and the Persian Wars (AD 226-363), p.122, p.138

[16] D. Van Berchem, L’armée de Dioclétien et la réforme constantinienne.

[17] E.N. Luttwak, The Grand Strategy of the Roman Empire, from the First Century AD to the Third

[18] B. Isaac, The Limits of Empire, p.170, pp.186-8

[19] D.S. Potter, ‘The Transformation of the Empire: 235-337 C.E.,’ p.158

[20] P. Sykes, A History of Persia, pp.33-5

[21] P. Sykes, A History of Persia, pp.37-8

[22] P. Sykes, A History of Persia: Volume 1, pp.488-503

[23] Aurelius Victor, liber de Caesaribus 39, 33-6, in M.H. Dodgeon and S.M.C. Lieu (eds.) The Roman Eastern Frontier and the Persian Wars (AD 226-363), p.126

[24] D.S. Potter, ‘The Transformation of the Empire 235-337 C.E.,’ p.158

[25] P. Sykes, A History of Persia, p.35

[26] D.S. Potter, ‘The Transformation of the Empire 235-337 C.E.,’ p.158

[27] B. Isaac, The Limits of Empire, p.372

[28] B. Isaac, The Limits of Empire, pp.252-60

[29] P. Sykes, A History of Persia, p.38

[30] B. Isaac, The Limits of Empire, pp.252-60

[31] D.S. Potter, ‘The Transformation of the Empire: 235-337 C.E.,’ p.158, K. Farrokh, Shadows in the Desert: ancient Persia at war, p.184


Primary Sources

Ammianus Marcellinus XXIII, 5, 2

Aurelius Victor, liber de Caesaribus 39, 33-6

Eutropius, breviarium IX, 2, 2-3, 1

Herodian VI, 5, 1-6, 6

Malalas, XII, pp.308, 17-22

Procopius, de bello Persico II, 5, 2-3

Secondary Sources

Dodgeon, M.H., and Lieu, S.M.C. (eds.), The Roman Eastern Frontier and the Persian Wars AD 226-363: A Documentary History (London, 1991)

Elton, H., ‘The Transformation of Government under Diocletian and Constantine,’ in D.S. Potter (ed.), A Companion to the Roman Empire (Oxford, 2010), pp.193-206

Farrokh, K., Shadows in the Desert: ancient Persia at war (Oxford and New York, 2007)

Frye, R.N., The Heritage of Persia (London, 1962)

Issac, B., The Limits of Empire: The Roman Army in the East (New York, 1992)

Luttwak, E.N., The Grand Strategy of the Roman Empire, from the First Century AD to the Third (Baltimore and London, 1976)

Pollard, N., ‘The Roman Army,’ in D.S. Potter (ed.), A Companion to the Roman Empire (Oxford, 2010), pp.206-28

Potter, D.S., ‘The Transformation of the Empire: 235-337 C.E.,’ in D.S. Potter (ed.), A Companion to the Roman Empire (Oxford, 2010), pp.153-75

Sykes, P., A History of Persia (Oxford, 1922)

Sykes, P., A History of Persia: Volume 1 (London, 1930)

Van Berchem, D., L’armée de Dioclétien et la réforme constantinienne (Paris, 1952)



Structure and argument:  Good. Argument is reasonably clear and quite well signposted. There is, however, an occasional tendency to make sweeping statements which are not borne out by the evidence. (e.g. ‘the Sassanians were seemingly able to raid at will into Roman territory.’).

Coverage and relevance: Good-Adequate. While four centuries is a large span to cover in 3,000 words, it remains the case that, despite occasional refs to later events, the main focus is very much on the 3rd and 4th century. Relevance maintained throughout.

Knowledge and understanding: Good-Adequate. Quite good, considering the relative unfamiliarity of the subject matter. Nonetheless, there are odd claims/statements (e.g. it is unclear how Hatra is relevant to Armenia, and who gained it as a protectorate; the peace settlement which in Rome gaining 5 provinces beyond the Tigris was in fact the same as the peace of Nisibis of 298/9 (rather than 297), a few lines later; Kobad did not reign in the mid-5th century; Noshirvwan’s first peace was in 532, not 531.

Use of ancient evidence: Good. Quite good use of Dodgeon & Lieu.

Use of modern discussions: Good. Quite a good range of material has been used quite well.

Referencing and bibliography: Good-Adequate. Referencing is reasonably thorough. Van Berchem is cited at n.16, but does not feature in bibliography. Format of referencing doesn’t follow a recognised system, though is clear enough as to details of sources. Bibliography of modern sources is fine. It is not usual practice to cite specific passages from ancient authors as Primary Sources: one would normally give the editions used; however, if as seems likely, these are cited from Dodgeon & Lieu, then this is the work that should be given here (rather than in Secondary Sources).

Spelling, punctuation, English: Good. Occasional careless typographical errors. Expression mostly fine.

General comments: Somewhat unbalanced in chronological focus, but a creditable effort.