Once the Normans had shown that they had control of England they had more time to build stronger castles. From about 1100 onwards stronger castles were built out of stone. These castles were known as square stone keeps because of their shape and the material they were built out of.

The stone was usually about 2 metres thick and they were built very tall so as to dominate the surrounding areas. This meant that the people inside the castle had a good view if anybody tried to attack them. Arrow slits were placed in the walls so that the defenders were able to shoot arrows out. These arrow slits were very small so that it made it difficult for the attackers to shoot arrows in. These arrow slits were always high up.

The Normans built large numbers of these castles all around the country. Some of the most famous square stone keeps can still be seen today. The White Tower at the Tower of London is one of the most famous. Another is at Rochester in Kent.

The square stone castle had problems too. The corners were its weakest area. Attackers soon realised that if they dug tunnels underneath, using wood to prop them up, once they reached the corners they could burn the props and the foundations of the castle would collapse, thus causing two walls to fall and allow the attackers on top to storm the castle. This was called undermining.

A square stone castle