The castle was no less prominent in peace than war, above all, of course, because it was the residence of the great, the centre and the seat of lordship, and this in an age of lordship when a ruling class really ruled. From first to last, as we have seen, the castle was a fortified residence: the residential function was no less fundamental to it than the military; and it was, indeed, this unique duality of residence and fortress that, so to speak, made a castle, and made it different from the fortifications of earlier and later periods. One may say also that it made it feudal, for while it is a matter of historical fact that the castle, the fortified residence of a lord, is the peculiar manifestation of feudal society, it is also entirely appropriate that it should be so. Feudal society, we are told, is society organized for war. It is also most certainly a society dominated by a military and a militant aristocracy, and what more appropriate setting could there be for them than castles? That the seigneurial residence should also be a fortress fits perfectly, and makes manifest, the military ethos of the age, as also do the seals whereon these aristocratic warriors formally represented themselves, or the effigies they had placed upon their tombs, in both cases armed cap à pie. Of course not every lord in the feudal period lived in a castle all the time, and not all lordly residences were fortified, i.e. were castles; but also there is no doubt that the castle became the symbol as well as much of the substance of lordship, and thereby an architectural concept meant to impress. Those castles depicted as rising on the skyline of the Très Riches Heures are real. And meanwhile, also, the castle as the residence of the lord (or his official) became inevitably the centre of local government, as we shall see, and sometimes other things as well, arising from its strength and social eminence.

There is one general feature of this medieval high society which must be noticed before any further discussion of the castle as its characteristic residence. Its members were almost continually on the move.

The military rôle of the castle is the most obvious, the most romantic, and basically the most important. Though the castle was always a residence no less than a fortress, and though from these two fundamental rôles others subsidiary followed, it was military necessity which first called the castle into being, whether at the time of its origin in ninth- or tenth-century France or whether in the England of the Norman Conquest, and military necessity which caused precisely that fusion of the lordly residence and the stronghold which is the peculiar characteristic of the castle. It is, after all, the degree of fortification which distinguishes a castle from a house. Warfare in the earlier centuries at least turned first and foremost upon the castle, and though from the later fourteenth century the military importance of the castle may have begun to decline, to read of wars in the chronicles of the eleventh, twelfth and thirteenth centuries is largely to read of sieges, while the surviving records of English royal government, for example, show beyond doubt that the maintenance of castles and their fortification and preparation for war were primary concerns of contemporary military organization. If we begin to ask why this was so, one fundamental answer – by no means widely understood since medieval warfare is a widely neglected subject – is that the military rôle of the castle was not just defensive but also offensive. Indeed we may argue that the latter is primary, for it was the offensive capacity of the castle, its function as a base, heavily defended, for active operations by means of which the surrounding countryside could be controlled, that gave it much of its value in war, made it the prized object of attack, and thus accounts for all those sieges. Only in this way, therefore, is the defensive role of the castle its most characteristic, though certainly it is the sieges which attracted the limelight of recorded events. Because the base and residence should be as impregnable as possible, it is defence also which, above all other considerations and requirements, dictated the castle's design and architectural form in the centuries of its supremacy in war, even though it had to fulfil as well its other functions as lordly and prestigious dwelling, centre of local government and administration, and, it might be, treasury, armoury or prison.