The great work of Viollet-le-Duc, though not confined to military architecture, contains by much the most comprehensive, as well as the most detailed, account of French castles yet given to the world; and as, besides the general resemblance between all European castles, those of the eleventh and twelfth centuries in Normandy are almost counterparts of those of the same period, and often built by the same nobles or their sons, in England, it has deservedly become our chief authority. Also the castles of France, being on a larger scale and often more perfect than our own, M. Le-Duc has been able to explain more satisfactorily than could have been done here, certain details, such, for example, as those of the gateway, drawbridge, and portcullis, and especially of the timber superstructures for vertical defence, known as “_hourdes_” and “_bretasches_,” terms represented with us by the “hoard” of a London builder, and the “brattice” of the mining engineer. M. Le-Duc’s work has given occasion and matter for a small volume from the press of Mr. Parker. There is besides a work in German, “_Geschichte der Militär-Architectur des fruhern Mittelalters_,” by M. G. H. Krieg von Hochfelden, which contains much of great interest concerning German castles, as well as a general notice of those in France and England. Although military architecture in England, setting aside the works of the Romans, begins with the age, and probably with the actual period, of the Norman Conquest, the country contains numerous examples of military works of an earlier, and in many instances no doubt of a very remote, time. These works, executed in earth, or at least of which no parts but banks, mounds, and ditches remain, are sometimes of great size, but usually of extreme simplicity of plan. Of most of them, the Roman again excepted, the relative age is all that we can hope to ascertain, but even from this knowledge we are at present very far; and although it is probable that the simple encampments, of irregular outline, and on high ground, are the work of the earliest inhabitants of Britain, and those of circular or more regular outline, having higher banks, and placed in more accessible positions, are the works of the post-Roman period, yet the outlines are often so mixed, and the arrangement of the mounds and banks so alike, that it cannot always certainly be said what is sepulchral, what merely commemorative or monumental, and what military; what the works of the earlier or later Celts, what of the Saxons, what of their Danish conquerors, and sometimes even, though not often, what is Roman.