How does castle building chaged during the medieval period?

Question: How does castle building chaged during the medieval period!?
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Canterbury in Kent has the remains of two castles which demonstrate the change in building techniques between the early years of the Norman occupation and later medieval designs!.

The first, now known as "Dane John" (from the Anglo-Norman donjon, meaning a castle keep) is an earth mound originally with a small enclosed bailey to the north!. The mound or motte would have supported a small timber tower on top and both mound and bailey would have had a bank and ditch, the bank fitted with a timber palisade!.

This castle was built soon after 1066, along with similar earth castles at Rochester and Dover, to protect the route from Dover's port to London!.

During the reign of Henry I (1100 to 1135) a programme of rebuilding castles in stone began!. Canterbury's castle site was moved slightly to the west, so the original motte and bailey remained visible!. The new castle incorporated part of the city wall and consisted of a rectangular bailey with stone wall, with a strong stone donjon near the southwest corner!. This donjon had walls over 14 feet thick at the base and was about 98 feet by 85 feet, rising to a height of around 80 feet!.

Inside the donjon (keep) was a storage area at ground level, with a great hall and chambers above and living areas above that!. This stone castle remained in use well into the 15th century, demonstrating the benefits and longevity of stone structures compared to the earlier timber and earth type!.

For details of both of Canterbury's castles see
http://www!.canterburytrust!.co!.uk/schools!.!.!.Www@QuestionHome@Com

The only difference in castle building throughout history is the thicker and heavier building of outer walls , as heavy missile weaponry was invented eventually dying out when black powder mortars and cannon became the normWww@QuestionHome@Com

It changed with the invention of new weapons and siege machines!.Www@QuestionHome@Com

How!?Www@QuestionHome@Com