Between those last precise accounts of military engagements which antiquity has left us in small number, and what may be called the modern history of war, there lies a period of many centuries-quite 1400 years-during which the details of an action and even the main features of a campaign are never given us by contemporary recorders.Through all that vast stretch of time we are compelled, if we desire to describe with any accuracy, and at any length, the conduct of a battle, to "reconstitute" the same. In other words, we have to argue from known conditions to unknown. We have to establish by a comparison of texts and of traditions, and by other processes which will be dealt with in a moment, a number of elements which, where a modern action is concerned, numerous memoirs and official record often accompanied by elaborate maps can put clearly before us.