Here is a new article I found.
Left: Schematic View of a 14th Century Castle. Such a castle was characterized by height and verticality. (1) Ditch (possibly filled with water) creating an inaccessible zone around the fortress. (2) Gatehouse with portcullis (a large iron or wooden grating used to block the passage when released vertically) and drawbridge (provided with a raising-and-lowering mechanism to hinder or enable passage). (3) Tower, projecting combat emplacement also used as lodging and storage place. (4) Wall, also called "curtain." (5) Wallwalk protected by a crenelated breastwork on top of the wall. (6) Hoarding, also called "brattice", a wooden balcony fitted with apertures through which the defenders could throw down missiles on enemies. (7) Postern, or sallyport, a secondary access. (8) Pepperpot turret, a small watchtower or lookout post. (9) Bailey, the open courtyard with chapel, well, stables, and other lodging and service buildings. (10) Dungeon, or keep, the most powerful tower of the castle and the dwelling place of the lord.
...In theory the whole feudal pyramid of loyalty culminated in the king. But as the kings- until the 12th century* - were rather weak powerless rulers, political power was based almost entirely on force of arms. Anyone prestigious enough to gain followers, able to build a castle, and rich enough to garrison it could create his independent state and concentrate in his own hands military, political, juridical, and economic power within his tiny kingdom. Moreover, the holder of a court of justice gained both authority and income as fines paid by offenders went into his coffer. The working unit of government became thus the castellany - the land near enough to a castle that it could be protected, policed, and administrated by the lord of the castle. In the 10th century, most castles were motte-and-baily fortresses. Based on a Viking/Norman design these were made by digging a ditch and piling the dirt into an artificial motte or mound. The edge of the ditch and the top of the mound were fortified with wooden palisades. On the summit of the mound inside the stockade stood a wooden tower which was the residence of the lord and his household. At the foot of the motte there were shallower and narrower ditches and stockades enclosing a bailey, an area which was a small village with houses and workshops for the lord's servants as well as stables and other outbuildings. In case of danger the baily served as a place of refuge for the lord's subjects from the neighborhood: the peasants, their families, and stock...
Dieu Le Roy,
*I dispute this discription of kings, especially those of England, and France. Examples: Charlemagne, William the Conqueror, Henry II, Richard Coeur de Lion. But that is my reading of history.