Conversation so far:
where did the normans build castles and what did their castles look like
Norman barons built timber castles on earthen mounds, beginning the development of motte-and-bailey castles.
can you tell me more about the motte and bailey castles
A motte and bailey castle is a fortification with a wooden or stone keep situated on a raised area of ground called a motte, accompanied by a courtyard, or Bailey.

Question: why are the castles popular for normans
Self-contained rewrite: why are the motte and bailey  castles popular for normans