William the Conqueror had to make lots of changes to England to gain control.
The Domesday Book was a survey of everyone in England so the king knew what England was like, and how much tax he should be getting.
Castles were built to help defend the areas of land that the Normans now controlled.
The biggest change was the feudal system, the King was at the top with the most power, then the barons, then the knights, and the peasants at the bottom.