MOTTE AND BAILEY CASTLE:
THE motte and bailey castle was an early form of medieval fortification especially popular with the Normans in northern France and Britain during the 11th century CE. A single tower was built on (or partially within) the motte or earth mound while a courtyard area or bailey at the base was protected by a wooden palisade and an encircling outer ditch. Relatively quick to build, the height of the mound made the tower difficult to attack while the wall offered a place of refuge from opportunist raiders. For these reasons, the motte and bailey castle was especially useful in freshly conquered territories where the native population was still hostile to their new overlords. As stone resisted fire better than wood and defensive designs improved, castles evolved into more permanent structures with stone circuit walls and towers enclosing a more impressive inner stone tower or keep (donjon).
The earliest form of fortified camp was a simple wooden palisade, perhaps with earthworks, surrounding a camp (ringworks), sometimes with a permanent wooden tower in the centre. These had been common since Roman times and remained little-changed for centuries. Then, stand-alone wooden towers became a feature of defences in northwest France from the 9th and 10th centuries CE. These structures evolved into the more sophisticated motte and bailey castles, which were especially common in France and Norman Britain from the 11th century CE.