Originally because of the urgency needed to get them erected these structures were of wood but, as they were vulnerable to fire, quite soon the King insisted that they be built of stone. One of the first of these was the White Tower in the center of the Tower of London. These more substantial buildings soon became home to the Lord and his retainers. It is an axiom of military design that each improvement in design creates its own destruction as the attacker soon learns to overcome the latest technology. Thus castle building became a never ending program of updating to create defensive protection. The keep had its own curtain wall with watchtowers. These were originally built square but it was soon found that it was easy for an attacker to use the square shape to protect himself against defenders and also undermine the corners of the tower. A corner would be undermined and the whole area filled with wooden props to support it. Then pigskins filled with oil and fat would be placed in the cavity and ignited. As the flames destroyed the props so the tower crumbled. An example of this can be seen at Rochester where the undermining of one square corner tower is quite clear before it was rebuilt as round tower.
Castle building grew apace and it became necessary to protect the original curtain wall with its own wall culminating in castles like the Tower of London where there are several concentric rings. England became more settled and by the middle of the fifteenth century in Southern and Middle England except for the King and powerful barons the smaller landowner had found that a more peaceful country made the castle unnecessary. He had had found the castle drafty, cold and uncomfortable and created 'fortified manor house'. This still had strong walls for defense but also had larger windows and more doors while the interior was of wood, rather than stone, to make the whole warmer and a less confrontational design. From then on we get the development of the 'stately home' and palace without any defensive capabilities and from these in turn produced the great Tudor mansions of which Hatfield House and Penshurst Place are typical and in which defense has no part. Peace was now assumed and the history of English castle building reached its end.
In the north of England it was not so easy and until the reign of Henry VIII there were still border attacks. The castles remained strong and well defended until well into the sixteenth century. Thus for hundreds of years the Duke of Northumberland remained influential as much because of the soldiers he could muster as his personality.
CASTLES OF ENGLAND
Location : Kent
When William the Conqueror defeated Harold II at Hastings he headed towards Dover where the Angle-Saxons had already raised a burh. William improved this fortification by erecting a motte-and-bailey. Dover Castle has the most massive tower in Britain, an almost 100-foot cube with walls from seventeen to twenty-one feet thick. In 1216 the castle was besieged by Louis, son of the French king but saved when Louis returned to France.
Overlooking Dover Harbour, the shortest sea-route to the Continent it barred the way of anybody trying to invade England. Early in the 19th century Napoleon stood opposite on the cliffs of Calais and through his telescope surveyed Dover. With the British navy controlling the seas and the steep cliffs beneath the castle he decided against an invasion of England, immediately turned round and invaded Russia instead. Hitler followed the same pattern and again after contemplating the problem decided to invade Russia instead. Beneath the castle are the secret wartime passages where the evacuation of Dunkirk and the Channel sea battle was controlled.