In western Europe in the ninth century, the breakup of the Carolingian
empire made the need for personal protection and fortified homes
necessary again. The amount and intensity of local warfare increased, and
later the attacks of the Vikings from the north and the Magyars from the
east made the defense of borders mandatory. In the ninth century the
Norse Vikings, masters of the hit-and-run offense, dedicated their skills
to ship building and erected relatively light fortifications. They built circular
base camps and trading centers that became true cities. When in
the tenth and eleventh centuries these Northmen settled in northern
France and began to fortify their holdings, they continued to build in
earth and timber. They developed the motte and bailey castle, a form
popular with the Germanic peoples all over Europe but most often associated
today with the Normans.