The Normans take control
The English did not want a Norman king. There were revolts, but William crushed them. Men who fought against the Normans were killed, and so were their wives and children. The Normans pulled down their homes and set fire to their crops.
The Normans built castles in all the main towns and in many villages. Castles were places where the new Norman lords could live in safety. And it was from the castles that Norman knights rode out to punish the English when there was trouble.
At first, they built motte-and-bailey castles. The bailey was a mound of earth, protected by a ditch and a wooden stockade, with wooden huts inside. This is where the Normans normally lived. If the English attacked, and broke into the bailey, they would retreat to the motte, a higher mound, with a wooden tower on top.
After a few years, the Normans began to build stone castles. Instead of a wooden tower, they built a keep. This was a high stone tower with thick walls so strong that many keeps are still standing.
Walter Robson: Medieval Britain; Oxford University Press, 1991/2000, page 5