During the 12th century many castles were improved and strengthened by using stone as the ain building material.
The wooden defences of motte and bailey castles were replaced by walls and towers of stone.
The methods of attacking and besieging castles improved over time and so became a need for stronger, more durable (longer lasting) defences.
Even though timber was strong against spears and arrows, fire could render it useless. Stone is more durable and resistant than wood and so it became the preferred building materials for castles.
Stone castles were built taller and gave better protection against attack, fire and cold rainy weather.
Stone castles replaced the motte and bailey castles but the stone castles also changed over time.
The rectangular Keep
Shortly after the Normans invaded England, they began building rectangular stone keeps. The White Tower at the Tower of London was started in 1070.
The first castles of stone consisted of rectangular towers surrounded by high stone walls.
The rounded Keep
Later, castles with round towers were built.