In This Article Expand or collapse the "in this article" section Roman Empire

  • Introduction
  • General Overviews
  • The Experience of Battle
  • The Army and the Imperial Economy
  • The Army and Society
  • The Army at War and in Politics

Military History Roman Empire
David Potter
  • LAST REVIEWED: 30 July 2014
  • LAST MODIFIED: 30 July 2014
  • DOI: 10.1093/obo/9780199791279-0123


The army was the central institution of the Roman Empire. It was during the Augustan Age that the Roman army was transformed from the agent of conquest and tool in the struggle for political dominance to an institution whose principal military role was defense against outside threats and deterrence of domestic unrest; its primary political role was to ensure the status quo of an ordered state—a role that it largely filled until the chaotic years of the 3rd century CE when the army once again became a tool in the hands of aspirant dynasts. Although armies had been stationed for long periods in the provinces during the Republic, the creation of an empire-wide entity with set terms of service, a coherent pay scale, and centralized control of command defined the structure on which the stability of the state depended. The governing principle appears to have been finance. As wealthy as Augustus was and as better organized as the state might have become, Augustus could not spend money he did not have over the long term—the post-Augustan army was melded with the tax system that supported it. The post-Augustan army differed from Republican armies in terms of its military strength as well as its mission. The Republican and Augustan armies were primarily recruited from peninsular Italy. In the course of the 1st century CE, recruitment shifted to the provinces. Additionally, new provincial units were recruited to act as auxiliaries, initially under leaders from the communities from which they were drawn (a continuation of Republican practice). After the civil wars of 69 CE, it became clear that this was an unwise practice, and officers for auxiliary units were drawn from the same pool of imperial aristocrats as the legions. Auxiliary units served under somewhat less favorable terms than did soldiers recruited into the legions, and all provincial units were less favorably treated than were the imperial guard units that were formed into the praetorian guard under Augustus. Unlike the provincial armies, the praetorians often played a significant role in determining the imperial succession. Major areas of ongoing debate and research include the nature of the Roman strategic thinking; the experience of battle; the impact of the army on the imperial economy, both on macro and regional scales; terms of service; officering and recruitment; the relationship between the army and civilian society; and the creation of a specifically military culture. The role of the army in politics is a final topic of considerable importance, both in terms of the structure of political society and in terms of the way in which Roman writers wrote about their army.

General Overviews

Numerous general accounts of the Roman imperial army are available. The works cited here are representative of recent developments in the field and offer a selection of works that may enable the nonspecialist to gain access to the field. Ritterling 1924 remains a valuable resource and was foundational for later study of the Roman army as it brought together the evidence for all the legions. It also enshrined a “legions-first” approach to the study of the Roman military. Pollard and Berry 2012 is a user-friendly and efficient update of Ritterling 1924, whereas Le Bohec and Wolff 2000 is a much more detailed update. Le Bohec 1994 and Southern 2006 are very fine surveys of the Roman imperial army, concentrating on issues of organization. Erdkamp 2007 provides a range of studies on both the Republican and imperial armies and is an indispensable guide to a wide range of issues in the study of the Roman military. Whereas Sabin, et al. 2007 covers the span of Greek and Roman history, individual contributions on the imperial period are fresh and insightful, such as Campbell and Tritle 2013 which offers a series of synoptic chapters focusing on issues in warfare across antiquity.

  • Campbell, J. B., and L. A. Tritle. The Oxford Handbook of Warfare in the Classical World. New York and Oxford: Oxford University Press, 2013.

    DOI: 10.1093/oxfordhb/9780195304657.001.0001

    General survey of warfare in the ancient world, Greek and Roman, with synoptic chapters on general subjects, ranging from archaic Greece to the Roman Empire and some more specific chapters on warfare in the Roman Empire. Especially useful for long-range issues even if less focused on issues that are especially relevant to the Roman Empire than other general surveys are.

  • Erdkamp, P. A Companion to the Roman Army. Malden, MA, and Oxford: Blackwell, 2007.

    DOI: 10.1002/9780470996577

    Covers the Republic to Late Antiquity, but divides chapters on specifically imperial topics from the other periods. Chapters 11–25 (pp. 183–476) deal with the empire. Chapters offer useful surveys of specific issues but do not shy away from making significant contributions to the areas that they review. Important, up-to-date introduction to the subject as a whole, with a welcome stress on material culture that is not present in all such volumes.

  • Le Bohec, Y. The Imperial Roman Army. Translated by Raphael Bate. London: B. T. Batsford, 1994.

    The English translation of the author’s L’armée romaine sous le Haut-Empire (3d ed. Paris: Picard, 2005) is a lucid and invaluable study of the imperial army, beginning with a discussion of its underlying structures—starting with its organization, the sort of people who were recruited, training, tactics, and strategy before giving an outline of the army’s role in the empire’s history, its function, and cultural influence.

  • Le Bohec, Y., and C. Wolff, eds. Les légions de Rome sous le Haut-Empire: Actes du Congrès de Lyon (17–19 septembre 1998). Paris: Diffusion de Boccard, 2000.

    An important collection of articles on the history of each legion in the Roman imperial army. The collection updates Emil Ritterling’s masterful article, “Legio,” in Ritterling 1924. Individual articles were contributed by a wide range of authors.

  • Pollard, N., and J. Berry. The Complete Roman Legions. London: Thames & Hudson, 2012.

    User-friendly, efficient, and thoroughly up-to-date account of the Roman legions. Although directed to a nonscholarly audience (and splendidly illustrated), the book is an important introduction to the subject for any student of the Roman world.

  • Ritterling, E. “Legio.” In Paulys Realencyclopädie der classischen Altertumswissenschaft: Neue Bearbeitung. Edited by A. Pauly, G. Wissowa, W. Kroll, K. Witte, K. Mittelhaus, and K. Ziegler. Stuttgart: J. B. Metzler, 1924.

    For some time the starting point for any study of the Roman imperial army, a brilliant collection and analysis of the evidence for all the legions of the imperial period, organized legion by legion. Although now replaced by Le Bohec and Wolff 2000, it had a significant impact on the study of the Roman military for the better part of a century. See cols. 1894–1980 cols. 1211–1829.

  • Sabin, P., H. van Wees, and M. Whitby, eds. The Cambridge History of Greek and Roman Warfare. 2 vols. Cambridge, UK, and New York: Cambridge University Press, 2007.

    Volume 2 (Rome from the Late Republic to the Late Empire) offers a topically arranged, often insightful, introduction to Roman warfare in the late Republic and the Empire. Subjects include international relations, military forces, types of wars, the experience of battle, warfare and the state, and warfare and society. The chapters on the historiography of warfare (pp. 3–81) in Volume 1 (Greece, the Hellenistic World, and the Rise of Rome) are also of general relevance with Michael Whitby’s chapter, “Reconstructing Ancient Warfare,” an especially important discussion of the literary sources (pp. 54–81).

  • Southern, P. The Roman Army: A Social and Institutional History. Santa Barbara, CA: ABC-CLIO, 2006.

    The introduction offers a helpful discussion of the sources followed by a discussion of the army’s development from the late Republic to the Empire. The third chapter (pp. 87–141) discusses the army, including discussion of the officer corps and recruitment patterns for legionaries and auxiliaries. Includes good discussions of the army’s culture and field operations (including an extended discussion of weaponry). The concluding chapters deal with the army of the Later Empire and famous Roman soldiers.

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