Because his domain was flat, the king ordered the construction of an artificial mountain to build his castle, this was called a motte.
Walls were added around the castle to protect the people from the invaders. There was usually a walkway running along the top of the walls, from which the castle guard could keep watch.
The walls were thick and had small windows, big enough for arches and arrows. Between the walls and the castle there was an open area called the bailey.
Towers were built at intervals along the walls, to strengthen them and also to give extra accommodation for castle workers.
You could also find ditches filled with water and were closed by a drawbridge that could be raised from the inside of the castle. In the inside of the castle were the living apartments, a well for water and food necessary to last for a long siege.