Anglo-Norman Military Architecture

Structures in early Norman castles were usually built of timber. None of them exists today, but a few surviving church towers of the period suggest the keep, at least, might have been a very sophisticated building. The use of stone became common in the 12th century as castles became permanent features in the landscape and had to resist improving siege techniques. Typically, a stone wall of the period was built above a solid trench-built foundation of mortared rubble. This was also used for the core of the wall itself which usually had a facing of neatly cut blocks.

The first structure to be built, or rebuilt, in stone was usually the keep which was set at ground level, as an earthen motte would not bear its weight. The keep at Colchester (c. 1070-1) and the White Tower at the Tower of London (c.1080) are early examples, although they were as much royal palaces as purely military buildings.

The classic Norman stone keep was a fortified tower with a near square ground plan. Inside, the main rooms were stacked one above the other and the ceilings often employed the new vaulting techniques of the period. On the ground floor there was usually a store and prison and on the first floor was the hall used for public business and accessible through the main entrance, often approached byremovable wooden stairs.Above the hall was the lord's private suite. There were recesses in the walls for cupboards, fireplaces and even latrines. Around the roof ran a wall walk protected by a crenellated parapet. Stone was also used for the castle's gate house and outer wall on account of their exposed position in any attack.

New ideas on military architecture in the late 12th century included keeps with plans of polygonal or circular form with outer buttresses. In theory they were stronger and needed less masonry than a traditional keep. In addition, there was a greater use of towers on the curtain wall than hitherto and outside the wall defensive ditches were greatly increased in size.