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.
why are the motte and bailey  castles popular for normans
Motte and bailey castles were relatively easy to build with unskilled labour, but still militarily formidable.
where in europe were the motte and bailey castles
Motte and Bailey castles were built across northern Europe  spreading from Normandy and Anjou in France, into the Holy Roman Empire.

Question: when were the castles built
Self-contained rewrite: when were motte and bailey castles built