When it was more peaceful, the Normans replaced the wooden fence with a stone wall. New stone castles were built and the old wooden ones pulled down. Stone buildings were usually too heavy to build on the motte so they were put in the bailey instead.

These stone towers were called keeps. Some of them were huge. The one at Rochester is over 34 metres high and its walls are over 3? metres thick. This was so wide that you could fit a car in the wall and still have space left over.

During the 12th century many castles were improved and strengthened using stone instead of wood. Many ideas for improving defences came from the east.

Concentric castles from the later middle ages show this. These castles had one walled enclosure built inside another. More complicated designs saw more and more walled enclosures inside one another, each improving the strength of the castle even more. Edward I used castles like this to secure his position in Wales.

Rochester Castle - Kent

There was a motte and bailey castle at Rochester soon after the Norman Conquest. The Domesday book (1086) speaks of land in Aylesford being given to the Bishop of Rochester in return for land on which the castle was built. In the Conqueror?s time both the city and the castle of Rochester were given to Odo, Bishop of Bayeux. Odo rebelled against William Rufus in 1087, and Rufus laid siege to the castle which was compelled to seek terms.

The keep at Rochester is 70 feet square at the base and rises to 113 feet high at the level of the parapet. The four angle turrets are a further 12 feet high. The walls are of Kentish ragstone with Caen stone dressing. The walls are 12 feet thick at the base, narrowing to 10 feet at the top.

The entrance to the keep was at first floor level, which was the level of the constable?s hall The ground floor was used as a storage room and all goods had to be carried up to the first floor entrance and then down the stairs to the ground floor. The main hall level was the second floor. This level is actually two stories in height and has a mural gallery running around the hall. At the level of the main hall the dividing wall is pierced with arches. The third floor housed the private chamber of the archbishop. There is some evidence to suggest that the archbishop had a private chapel at this level.

In 1215 the castle was besieged by King John and the south east tower was slighted. It was rebuilt again with a round tower instead of a square one