When a Keep was added to a castle of the Motte and Bailey type there does not appear to have been any regular rule as to its position. At Guildford it was erected upon the motte (though a little way down the slope), and also at Nottingham, Pickering, and York; at Clun in Shropshire the Keep was built partly on the motte, occupying the eastern slope, the mound apparently bearing a defence of the Shell Keep pattern at the same time. Gloucester Castle has been entirely destroyed in order to make room for a modern prison, but from existing records we learn that the Keep was an addition, occupying the centre of the former bailey, while the building at Newcastle also stood distinct from the mound. The Keep at Oxford stands upon the enceinte at some distance from the Shell Keep, while at Rochester and Canterbury the new additions were erected outside the original castle. [Illustration: CLUN CASTLE, SALOP.] In the reign of the Conqueror and his immediate descendants, the rapid building of castles for overawing the defeated Saxons was a matter of Crown policy, but with the settlement of the Kingdom, and the rise into power of Norman nobles waxing rich and powerful upon their estates, restrictions became imperative if the royal prerogatives were not to be set at nought. Consequently, special licences to build and crenellate had to be obtained before erecting, or adding to the existing defences of, a castle, and the rigorous insistence upon this law was readily recognised and maintained by all strong rulers of the kingdom. When, however, a weak monarch came to the throne, or internal dissensions occurred, the Norman barons invariably seized the opportunity thus afforded, and a large increase of these fortalices sprang into existence. The most remarkable example was during the eighteen years of strife wherein King Stephen was struggling for his crown with the forces of Queen Maud. In order to propitiate the nobles and secure their services, the King gave licences with a reckless indifference to consequences, and many scores of castles were erected under these permissions, but a still greater number with no licence at all. These latter became known as "adulterine" or spurious castles; the total number built during this period of anarchy is said to have been more than one thousand, but more modern computation places the number at about seven hundred. Stephen, when too late, perceived the mischief attending the multiplication of these citadels, and attempted to reduce the evil by destroying those belonging to the clergy. The essay proved to be a mistake, and during the disorder that ensued, the land became a prey to anarchy of the most violent kind, each baron or leader of mercenaries doing that which was right in his own eyes, and retreating to the safe precincts of his castle when in difficulties.