The subject of this thesis is a collection of military handbooks or tactica produced in the East Roman Empire in the 6th century. Although all these texts are discussed in turn, the study naturally concentrates on the two largest works, the "Compendium" of Syrianus Magister and the Strategikon attributed to the Emperor Maurice (582-602). The approach to these tactica has been on a number of levels. The first half of the thesis is primarily a textual study, which examines the inter-relationships between the 6th century works, their probable dating and authorship and their manuscript transmission. There follows a detailed analysis of the extent to which they were influenced by earlier works within this literary genre, which dates back to the 4th Century B.C., and the manner in which this traditional material was adapted to the military circumstances of the 6th century. These classical influences, both stylistic and conceptual, are balanced by a study of the influence exerted on East Roman military theory and practice by neighbouring peoples, particularly those relatively new to the Empire's cultural sphere, notably the Avars and the Turks. This involves an examination of the processes by which military technology and techniques were diffused between pre-industrial societies, and the extent to which the Romans actively studied the military methods of their enemies. This study is set within the context of a long-standing Roman tradition of military eclecticism. Having assessed the degree of traditional and empirical content, the thesis then compares the theoretical precepts of the textbooks with the military practices described by contemporary historians and chroniclers, with a particular regard to the development of tactics – how Roman armies prepared for and engaged in combat. By such a comparison the thesis aims to establish the relationship between theory and practice, and ultimately to provide an assessment of the practical utility of this sort of technical literature in Late Antiquity.