From Wood to Stone
The first castles were made of wood, but after the threat of vulnerability to fire was realized, stone became the material in which castles were constructed. Although stone was very stable and secure than timber, it took much longer to build these castles because of the resources and time required to shape the stone.
Natural features around castles were of significance because they provided additional security. Moats, a ditch surrounding the castle filled with water, are probably the most well-known feature of later castles. The water sometimes contained dangerous animals such as alligators. Other natural features included rivers and ditches. Sometimes the ground was modified to form “motte and baileys” and “ringworks.” Mottes were simply raised ground on which a tower stood. A bailey was “a large, level enclosed area beside the motte, surrounded by an earthwork bank and ditch, topped with a timber palisade” (Robins).
The first stone castle known-to-date was built in about 950 A.D. at Doué-la-Fontaine, France (Robins). Common shapes used for stone castles included rectangles, circles, squares, multi-sided polygons, and D-shapes. Stone towers, called “keeps,” “great towers,” or “donjons,” were often built as part of the castle. Rectangular-shaped castles sometimes had four towers - one at each corner. Average castle walls were ten feet thick, but some walls were up to three times that. This incredibly thick wall did an extremely good job of keeping enemies outside.
Concentric castles (castles with an extra wall or "ring" surrounding them) became popular because they literally added another layer of protection. A main reason these were implemented was because there could be two sets of soldiers on each of the walls (outer and inner) during a battle, and both could shoot at the enemy. The inner walls were made higher so that the soldiers on the inside wall did not shoot the soldiers on the outside wall (Sierra). See Example Here »
Photograph Credit (above): Ulldecona Castle (Flickr)
Image Credit: Parts of a Castle (Parts of a Castle)