Deploying a Roman Army: The Ektaxis kat' Alanōn of Arrian

by Duncan B. Campbell

The Ektaxis kat' Alanōn ("Deployment Against the Alans") is a work of unusual importance written by the Roman consul Arrian. It takes the form of a series of instructions, whose aim is firstly to assemble into marching order a variety of individually named military units (identifiable as part of the Hadrianic garrison of the Roman province of Cappadocia), and secondly to deploy them in line of battle against a mounted foe, the Alans of the title. A third section then gives advice on how the battle should unfold.

Only a single copy of the work survives, preserved in a tenth-century manuscript, and the Greek text has required occasional emendation in order to clarify Arrian's original meaning. This volume presents an improved Greek text, the first since 1928, with a Loeb-style facing-page English translation. As well as an in-depth introduction to Arrian, his work, and his governorship of Cappadocia, there is also, for the first time ever, a detailed 130-page commentary on the Ektaxis . The volume is fully indexed and will be of interest to students and scholars of Arrian, as well as Roman army enthusiasts.

228 pages, Paperback

Published June 2, 2022

About the author

Dr Duncan B Campbell is a specialist in Greek and Roman military history. He first became fascinated by Roman archaeology after a childhood visit to Hadrian's Wall. He published his first academic paper in 1984, as an undergraduate at Glasgow University (Scotland), and produced a complete re-assessment of Roman siegecraft for his PhD.
He has made some of his research accessible to a wider readership through Osprey's New Vanguard, Elite, and Fortress series, and he is a regular contributor to *Ancient Warfare* magazine. Besides writing occasional academic articles, he is a frequent reviewer for *Bryn Mawr Classical Review*.
In his latest book, *The Fate of the Ninth*, he discusses the curious disappearance of Rome's Ninth Legion.

Reviews

[Jonathan F · Rating 5 out of 5]

The Deployment Against the Alans is very short and Arrian's work focuses on two main components: the organization of his force on the march and its deployment on the battle line. That's it.

It's pretty interesting for three reasons. First, it took me some reflection to understand the work's significance.

Second, it's written as a piece of literature. Arrian is inspired by the classical Greek historian Xenophon, the Athenian general who wrote an eye-witness account of the Greek mercenary participation in the failed usurpation of Artaxerxes II and a history of the late Peloponnesian War down to the Arcadian victory at Mantinea. He's in good company there. Xenophon was a philosopher, something Arrian was too. And by adopting his synthesis of Xenophon's style, he used his writing to communicate his command of "the literature," so to speak.

Third, embedded in what is a very straightforward description of an army on the march and in battle formation, is the much more important description of how the governor of a Roman province formed a field army during the height of the Principate — under the imperial rule no less of an emperor than Hadrian. And in understanding this the commentary is invaluable.

The commentary is great. Although it's frequently technical and focused on the interpretation of certain Greek words, the author does a good job of inserting a lot of ancillary knowledge. This includes the stories of specific soldiers, commanders, and governors, told through the epigraphic evidence.

Because Arrian is writing in the style of Xenophon, he uses a more...artistic language. Like things as innocent as calling the Legio XV Apollinaris the "Fifteenth Phalanx." And more confusingly, the "Petraian horse archers," who are the cohors III Ulpia Petraeorum miliaria equitata — a 1,000-man auxiliary force on horseback, originally raised by Trajan in Arabia Petraea. The author does a fantastic job giving you the historical context. Arrian also refers to himself as Xenophon, and his commanders are given names like Demetrius and Valens. Presumably, his immediate audience would understand the references to the actual officers in his army.

What you get is an implicit description of how a Roman governor, in command of a pretty significant military force, prepared for battle. Arrian commands two legions, auxiliaries, and allies, similar to the consular army of the early-to-mid Republic. Furthermore, by associating the units in Arrian with their counterparts, and given them as much context as possible in terms of their potential geographic distribution during peacetime, you can build a picture of what it meant for a Roman prefect to form a field army.

Only one legion was complete, the other one was understrength as 35–45% was left in their base, besides ad hoc units splintered off to occupy various fortifications or perform various duties. Some auxiliary units came only in part, as well. A good Roman governor doesn't strip his borders of all of its defenses. Many units did come in full, as well as militia units from northeastern Pontus, units from presumably autonomous vassal states along the frontier zone with Armenia, and finally allied contingents under Arrian's command.

Arrian is marching to meet an Alan invasion of the frontier province of Cappadocia, secured by the aforementioned army. At peacetime, this army is distributed to major bases, smaller forts, and a string of fortlets that seek to deny access to Roman frontier space and allow for the efficient mobilization of a significant field army. This army is expected to defeat incursions of foreign forces into the province, or at least tie them down until the emperor arrives with reinforcements.

The geographic distribution of the army during peacetime speaks to the active role that said army played in the day-to-day Roman frontier defense. The book that led me to The Ektaxis is David Breeze's, The Frontiers of Imperial Rome — I review that here. Not just auxiliary units, but ad hoc units splintered off the legions also participated in the occupation of border fortifications to oversee the major access points along the frontier zone. Denying access is an important component of defending against foreign incursions on the borders. Beyond this, small Roman military units are also invariably deployed in caravan protection and patrol into allied and vassal territories.

The variety among these units is not trivial. Roman armies during the empire were not just composed of heavy infantry, or even necessarily. Arrian counts on significant numbers of cavalry, horse archers, foot archers, militia spearmen, artillery in the form of onagers and scorpions, among other varieties of auxiliary units. His is a combined army and his strategy comes down to shock-and-awe, along with a contingency plan if the Alans try to get smart by flanking his force.

Although the bulk of the two legions are available, putting together his field army requires Arrian to reduce the forces available to do all the things those same units already do. He has to strip the frontier of its defensive forces. Of course, as a good governor, he leaves significant forces behind to continue their normal duties, although perhaps more overstretched.

The reason why I find this so interesting is because it gives you context on what it may have meant to the geographic zone of mobilization when a Roman provincial commander launched a usurpation. Concentrating forces to meet a foreign invasion makes a lot of sense. You're stripping the frontiers temporarily, but you are decisively defeating a major foreign threat. In most cases throughout Roman history, successful. In many cases, not so much. And in some, with absolutely disastrous results.

Roman governors didn't just mobilize field armies to fight foreign invasions, though. They also launched and defended against domestic threats. These include usurpation attempts. Arrian indirectly gaves you a sense of the logistics involved in forming a major mobile force capable of waging decisive battle. The commander would need to draw from a wide range of local military units, and likely local recruits called up in the form of imperial direction to raise militia and allied units from local cities and autonomous governments. It represented a major endeavor in terms of manpower concentration.

It's often noted in histories of the late imperial army that bases for the comitatenses have yet to be found. And there is ample archeological evidence of the frontier fortifications along the Rhine and Danube Rivers, so it's definitely significant that a base capable of housing a field army has yet to be found. If these field armies were put together from disparate pieces in the moment of action, then a major permanent field unit-sized base is not necessary.

And if late imperial Roman field armies were mobilized in the same, or similar, way as Arrian's, you get a powerful view of the significance of usurpation. During a usurpation, typically, a local Roman provincial commander formed a field army and either drew the incumbent emperor into their territory or marched out to seek him. The Roman army was primarily deployed along its frontiers. Auxilary units and legionary splinter units are physically controlling access points through the frontier zone. These have to be mobilized to significantly increase a powerful reserve force, formed by the bulk of the legions based in that province.

When Constantine III formed a significant field army in Britain in 407 and crossed into Gaul, challenging Honorius, or rather Stilicho, the drain of Britain's frontier defenses must have been devastating. Small wonder the island is permanently abandoned. Constantine may have had as many as 30,000 soldiers, like or larger than your early-to-mid consular army. Britain had three legions. But more than half of those men had to be taken from frontier duties. Likewise, imagine what the loss of Eugenius' (and much of Theodisius') army at Frigidus in 394 meant in terms of heavy manpower losses to frontier units that depended on them.

It also gives you context on why some usurpation attempts may have failed. One example is Gildo's against Honorius, or rather (again) Stilicho. In this case, Gildo's claim in Africa is defeated by a local commander empowered by Stilicho, implying a division of loyalties within frontier military units.

Just more generally, it's interesting to think about the machinery of the Roman army within any context of its military history. This includes simply thinking through the mobilization of field armies to invade across the frontier. Imagine the forces that Marcus Aurelius commanded to defeat the Marcomanni. He had large legionary forces, otherwise deployed as major reserves along the frontier, and likely an even larger auxiliary force. Or think of how Trajan formed successive field armies, first to invade Dacia, then Armenia, then Mesopotamia. Not to mention his conquest of Arabia Petrea. Some of the units formed to fight these wars and secure the conquests were used by Arrian in Cappadocia.

Think about the Rhine frontier during the late empire. We know that the nature of the Roman army did change between and during the high empire and the late empire. The old auxiliary units start to disappear in that name. In some places, like the Rhine frontier, the local defensive forces are drawn from a group of frontier peoples who by law are expected to mobilize forces from among themselves to meet a foreign incursion. This group is very commonly, into the late empire, composed of transborder 'barbarian' forces settled along the frontier zone instead of other domestic forces. And it's commanders of foreign descent (the Roman-born children of foreign warlords), and at the very end the foreign warlords themselves, who were increasingly directly involved in these usurpations. If they held high command in these usurper's armies, it's because they commanded significant forces.

Imagine then what the loss of Arbogast's army at the Frigidus meant to the Rhine frontier defenses. If frontier units were getting smashed in civil wars, their frontier duties had to be given to someone else. It makes sense for emperors to increasingly turn to, essentially, mercenaries that might otherwise threaten to invade and take these frontier zones anyway. Or the checking of Stilicho's army by Constantine III, who stripped Britain of her defenses. And the significance of Alaric, his official command of Roman forces in Illyrium, which were Visigothic forces paid for and supplied by the Eastern Roman administration — how a gradual deterioration of frontier forces led to the paradox of Rome's eventual conquerors to be employed as mercenary field armies. Not to mention Stilicho, who still likely stripped Raetia of significant Roman frontier forces in order to field a sufficiently powerful field army to check Alaric in Italy (per Burns in Barbarians Within the Gates of Rome).

Anyway, I digress. Simply put, this is a book that deserves reflection.

[Robert · Rating 5 out of 5]

HFS, this is awesome. Campbell presents a new English translation and a very detailed discussion of this mid 2nd century AD document, explaining both Arrian's stylistic use of Greek words, and how other translators emended, and translated this work, and why they got various things wrong.

Especially useful is Campbell's identification of the various bodies of troops in this army.

The discussion of the use of various Greek words is beyond me, not having any Greek, but it appears Campbell has definitely done his homework.

Recommended.