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Rh the Norman castles and about the Edwardian castles.

The Norman castle was a square keep, with walls of immense thickness, sometimes of 20 feet. But if the Norman had to build on the top of a hill or on the ruins of an old castle, he did not try to make the new castle square, but allowed its walls to take the form of the hill or of the old castle; and this kind of castle was called a shell keep.The outer and inner casing of the wall would be of dressed stone, the middle part was chiefly rubble. At first, if they had plenty of supplies, a very few men could hold a castle against an army as long as they liked. These were the castles built by the Norman invaders to retain their hold over the Welsh districts they conquered.

But many ways of storming a castle were discovered. They could be scaled by means of tall ladders, especially in a stealthy night attack. Stones could be thrown over the walls by mangonels to annoy the garrison. Sometimes a wall could be brought down by a battering-ram. But the quickest and surest way was by mining. The miners worked their way to the wall, and then began to take some of the stones of the outer casing out, propping the wall up with