Castles changed because new methods of attack came into place e.g. flaming arrows to burn down the keep; rope ladders thrown over the wall to allow climbing up, and cannons able to easily break down wooden walls and fences.

 

Some of the problems with using wood were that it rotted, could be burnt easily and was not strong enough to hold tall structures when attacked.  The biggest of these changes was therefore to build more from stone instead of wood.

 

Stone allowed taller towers and walls to be built that did not rot and would not burn easily. This made it harder to attack the castle.