A castle is a private fortress, built by an individual lord as a military stronghold, and also as an occasional residence. In England at the time of the Norman conquest, this type of military work was known as _castel_, a word which is obviously the same as the Latin _castellum_. _Castrum_, _munitio_, and _municipium_ are names which are frequently given to it by chroniclers of the eleventh and twelfth centuries. Its existence was the direct result of the consolidation of the feudal system. The lord separated his dwelling from those of his vassals: he defended it against the attacks of other individual lords who naturally would seek to aggrandise themselves at his expense: he also needed a stronghold which might be impregnable on occasion against those vassals themselves, and might be a perpetual reminder to them of their subject position. The castle rose within or as an addition to the _burh_, the independent stronghold of one person within the walled or stockaded town of the many. Thus, at one and the same time, it protected and overawed the _burh_. Or it rose by itself, like the Peak castle in Derbyshire, on a spot where no _burh_ existed, and so in many cases drew a small community to seek its protection. An unlimited number of castles implies an unlimited number of independent magnates, uncontrolled by a supreme authority, and each ready to fly at the other’s throat. The feudal lord, however, was the king’s man, and his castle was therefore theoretically the king’s. We have already noticed the edict of Pistes (864), which ordered the destruction of all castles built without royal licence; and, save in periods of total anarchy, legislation of this type, safeguarding feudal order, was in operation during the middle ages wherever the feudal system was at the base of the constitution. The king was _de jure_, if not _de facto_, the owner of the castles of his realm. The castle or private fortress was a feature in French social life and warfare from at any rate the middle of the ninth century. But in England it was certainly an unfamiliar and almost as certainly an unknown feature, until the middle of the eleventh century. Danish pirates who up to this time had visited England, had come from the north and east, and passed on to France. There, in contact with the feudal system as it existed under the later Carolingian monarchs, they may have learned the use of the private fortress. At any rate when the Northmen came back upon England from their continental duchy, they brought with them the fully organised social system of the Continent, and its most powerful symbol, the castle. [Illustration: Harold’s _aula_, from Bayeux Tapestry]