The Roman Legion

by

Jessica Clark

• LAST MODIFIED: 20 March 2025
• DOI: 10.1093/obo/9780195389661-0427

Introduction

Few subjects in ancient history have received as much attention as the Roman military. The legion is the best-known avatar of that military and was the Roman army’s longest-standing organizational unit and a proxy for its imperial expansion. Scholarship on the Roman legion is thus often inseparable from that on the Roman military more generally. Readers should consult the separate Oxford Bibliographies article “Roman Military” for surveys of general historical overviews, handbooks and companions on the topic, and primary sources. A Roman legion was both a means of organizing soldiers for combat and a subdivision of a larger army, and the term is used interchangeably by ancient and modern writers to denote only the fighting men and the collective of which they were a part. This elision results in part from the historical shifts that the legions underwent, from circumstantial levies to standing armies, and it is important to approach the study of any of the Roman legion’s particulars with attention to the phase of legionary history with which one is concerned, and to be aware when arguments must rely on evidence from potentially incompatible phases. Here, legionary history is divided into chronological subheadings (Historical Development of the Legions). The noun legio denotes simply a selection and gathering of men, and the term may have been used, in the singular, to denote the original army of the Regal period. In the Republic, each consul could command a legion, which might vary in size and organization depending on the needs of a year’s campaign. The term gradually acquired its formal connotations and more standard size and subdivisions, and infantry numbers increased in the late Republic and Empire. In the late Empire the term was used for significantly smaller units, and there is relatively little evidence for the distinct function of the legion (in its classical sense) in the fourth century CE. Throughout the Republic and Empire, each Roman legion was matched by an equal number of Allied or auxiliary troops. Scholarship on Roman legions generally focuses upon the Roman citizen soldiers (and sometimes only the regular infantry component) as constitutive of the legion’s identity. While the legion was, symbolically, this core of adult citizen men, it was also a larger community that included diverse non-citizen specialized combat units and civilians, both free and enslaved, who engaged in a wide variety of occupations. All were indispensable to the legion’s success.

General Overviews

Pollard and Berry 2012 is an accessible and well-researched introduction to the history of the legion as the means by which Rome organized its land forces and the individual histories of specific legions, and Campbell 1999 is a brief historical survey. Parker 1971 (originally 1928) is dated but still useful both as an overview and as a stage in the history of scholarship on the legions. Phang 2011 discusses scholarly themes and developments in Roman military history, with much on the legions. Wheeler 2004 debates legionary tactics. De Blois, et al. 2007 is a collection of scholarly papers on legions and Roman military culture. Speidel 2015 introduces epigraphic evidence for the legions. Fuhrmann 2012 and Potter 2014, Oxford Bibliographies in the Military History module, include a range of further introductory and thematic works.

• Campbell, J. Brian. 1999. Legio. In Der neue Pauly. Enzyklopädie der Antike. Vol. 7. Edited by Hubert Cancik and Helmuth Schneider col. 7–22. Stuttgart and Weimer, Germany: J. B. Metzler.

  A concise survey of the evolving definition and function of the Roman legion, with summary descriptions of individual legions and two maps, showing their distribution under Augustus and c. 200 CE. The print edition is in German; the (paywalled) online edition is offered in both German and English.

• de Blois, Lukas, Elio Lo Cascio, Olivier Hekster, and Gerda de Kleijn, eds. 2007. The impact of the Roman army (200 BC-AD 476): Economic, social, political, religious, and cultural aspects. Proceedings of the Sixth Workshop of the International Network Impact of Empire (Roman Empire, 200 B.C.-A.D. 476), Capri, March 29-April 2, 2005. Impacts of Empire 6. Leiden, The Netherlands, and Boston: Brill.

  This (currently open-access) collection of thirty chapters (in English, French, German, and Italian) provides an excellent orientation to the scope and variety of current approaches to Roman military history. While only a few chapters take a legion or legions as their explicit focus, all examine aspects of legionary history and culture, from recruitment and equipment to religious and economic aspects.

• Fuhrmann, Christopher. 2012. Roman army. In Oxford Bibliographies in Military History. New York: Oxford Univ. Press.

  Contains a wide range of general reference works for Roman history, as well as an overview of primary sources and important journals, aimed at orienting a non-classicist to the field of ancient Roman military history.

• Parker, Henry Michael Denne. 1971. The Roman Legions. Cambridge, UK: W. Heffer.

  This detailed and readable narrative of the development and individual (imperial) histories of the legions reflects the state of scholarship in the 1920s, and is interesting for its discussions of legionary recruitment, service, and officer corps as reflected by that early-20th-century context. Contains untranslated Latin. Reprinted with corrections. Originally published 1928.

• Phang, Sara E. 2011. New approaches to the Roman army. In Recent directions in the military history of the ancient world. Edited by Lee L. Brice and Jennifer T. Roberts, 105–144. Publications of the Association of Ancient Historians 10. Claremont, CA: Regina Books.

  A thorough survey of the state of scholarship on the Roman military, which can also serve as a good introduction to the topic and to legionary history and culture more specifically.

• Pollard, Nigel, and Joanne Berry. 2012. The complete Roman Legions. London: Thames & Hudson.

  This accessibly-written and impressively illustrated book includes a brief history of the development of Rome’s legions, from the mid-Republic through Late Antiquity. Individual chapters on specific legions focus on their imperial campaigns and the architectural and engineering legacies of legions’ permanent bases throughout the wider Mediterranean world. Ancillary materials, including timelines and suggestions for further reading, make this a particularly valuable introduction to legionary history.

• Potter, David. 2014. Roman Empire. In Oxford Bibliographies in Military History. New York: Oxford Univ. Press.

  In addition to key reference works that also appear here, includes sections on the historiography of the Roman military, material evidence, and aspects of strategy and command.

• Speidel, Michael Alexander. 2015. The Roman army. In The Oxford handbook of Roman epigraphy. Edited by Christer Bruun and Jonathan Edmondson, 319–344. Oxford and New York: Oxford Univ. Press.

  Focused on the army of the Empire, this survey of Roman military epigraphy and its contexts includes numerous examples and valuable discussions of methodologies and their limitations. It is accessible to undergraduates but will be of use to scholars at all levels interested in integrating epigraphic evidence to their study of the legions.

• Wheeler, Everett L. 2004. The legion as phalanx in the Late Empire, 1. In L’ armée romaine de Dioclétien à Valentinien Ier: actes du congrès de Lyon (12–14 septembre 2002). Edited by Yann Le Bohec and Catherine Wolff, 309–358. Collection du Centre d’Études Romaines et Gallo-Romaines n.s. 26. Paris: de Boccard.

  Despite its title, this article offers a critical synopsis of the ancient evidence for and modern debates about legionary tactics from the Republic to Empire; as these debates continue, this is a useful place for newcomers to that topic to orient themselves.