IMPERIAL DEFENCE IN THE FOURTH CENTURY WEST
This paper will attempt to use the detailed information available in the narrative history of Ammianus Marcellinus to explore the ways in which the Roman Empire defended especially its Rhine frontier in the midfourth century A.D. Ammianus served on the Rhine under the then Caesar Julian in the 350s, and clearly also had access to detailed information on events there in the reign of Valentinian I in the 360s and 370s. As a result, it is possible to follow evolving patterns of defence and shifting imperial policies almost continuously over a twenty five year period. The information concentrates for the most part upon the sector of the river bordering the Alamanni: the central and upper reaches of the Rhine, together with the upper Danube. The picture of imperial defence in this area is supplemented and amplified, however, by further material relating to the Franks and Saxons of the lower Rhine and its hinterland, together with the various groups opposite the Middle and Lower Danube. For these latter groups, Ammianus' information is less continuously detailed. It is sufficient, however, especially when taken together with material from other late Roman sources, to show that similar techniques were in fact employed by the Empire right across its european frontiers, all the way from the mouth of the Rhine to the Black Sea.
There is, of course, another, very well-established line of enquiry into late Roman defence: Limesforschungen. As the many and important volumes in the Limes Congress series indicate, the physical study of Roman imperial defences and their evolution over time has a long and productive history. The attempt to interpret these remains has likewise stimulated productive and vigorous debate, an important landmark being the influential monograph of Edward Luttwak, applying the viewpoint of a modern strategic analyst to the available information concerning forts and, if to a lesser extent, battles.1 But the process of re-animating
1 E.N. Luttwak, The Grand Strategy of the Roman Empire from the First Century A.D. to the
Third (Baltimore, 1976). The many volumes of the Limes Congress document this approach.