Castles were built over many centuries, so it is not surprising that their design changed, or that castles had new bits added from time to time.
You can tell the oldest castles because they have a motte, keep, curtain wall and bailey. They may have two rings of walls if these were added later.
'Younger' castles were built without a keep and have just two massive rings of walls.
Castles were built from the 11th right through to the 15th centuries.
