speed in their destruction, during the century following the Conquest, are easily explained if their works were merely of earth and wood. And it is thus possible that, when we meet with a mount-and-bailey fortress, unnamed in history and untouched by medieval stonemasons, it may be neither on a site chosen and then abandoned by an early Norman lord, nor a mere outpost of some greater castle, but a stronghold hastily entrenched and heaped up in time of rebellion, by some noble of the time of Stephen or Henry II., and dismantled when peace was restored, and the authority of the sovereign recognised. CHAPTER IV THE PROGRESS OF ATTACK AND DEFENCE The earthwork fortifications, the progress of which we have traced up to the Norman conquest, were of a very simple kind. It is obvious that, in the history of military architecture, any improvement in defence is the consequence of improved methods of attack. The stone-walled town of the middle ages, the castle or private citadel, with its curtain wall and the subdivision of its enclosure into more than one bailey, succeeded the palisaded earthwork as a natural result of the development of the art of siege. Against an enemy whose artillery was comparatively feeble the stockaded enclosure was effective enough: slingers and bowmen, working at close quarters, might do damage to the defenders, but the palisade on the bank, divided from the besiegers by a formidable ditch, was proof against missiles launched against it by individuals, and could be carried only by a determined rush, or if it were not sufficiently protected against fire. Modern warfare against uncivilised tribes has shown that a stronghold defended by a thick hedge is a serious problem to a besieging force. If, under modern conditions, the stockade is a barrier to troops equipped with powerful firearms, the difficulty which it afforded to the early medieval warrior is obvious.