Castles were a major stronghold, designed to defend a nation and its king from an invading army. As time and technology advanced, early castle models were improved with thicker walls and intelligent design. During siege warfare, the castle walls were all that stood between victory and defeat. Victory meant the walls were able to withstand the relentless efforts of the invading army to bring them crumbling down; defeat meant the death of the king.
Motte and Bailey Castles
The motte and bailey castle was most prolific during the 10th and 12th centuries, and were the earliest castle form in Europe, according to medievalcastles.stormthecastle.com. The Motte is a large mound of dirt where the keep would stand; the bailey was a large courtyard surrounded by fence or wall, which was typically made from wood. Two ditches -- one small and one large -- were dug out around the perimeter of the fence. The dug-up soil was used to make the Motte. A wooden drawbridge was usually constructed to make crossing the two ditches easier. The ditches also made it difficult for an attacking army to get close to the castle wall.
The Rectangular Keep
The rectangular keep, primarily built between the 11th and 12th centuries, is more in line with how people tend to imagine a castle. Four very high stone towers were built at each corner of the rectangular shapes. The towers were then connected by a thick, slight lower wall. These castles required a flat surface for construction because the weight of the stone and height of the walls required a stable foundation. The entrance was built on the second floor and a narrow staircase lead up to it. As a result, the high entrance made it difficult for enemies to breech the castle doors.
Concentric castles, built between the 13th and 14th centuries, were a more advanced and well thought out design in comparison to the previous two castle types. Essentially, a concentric castle was a keep surrounded by a high wall, which was surrounded by another wall. Sometimes a moat was created between the two walls to create another line of defence if the first wall failed. Furthermore, the keep and inner towers were built as rounded structures, rather than square blocks, because rounded structures were better able to withstand attacks. Additionally, square-shaped towers created blind spots where attackers could exploit; round towers eliminated this problem.
Castle construction evolved as time proved that construction and design were no longer able to offer protection. The motte and bailey castle was soon replaced because enemies were able to easily burn down walls with the advancement and use of fire as a weapon. In addition, as weapons advanced -- such as the invention of the catapult -- towers and walls required additional height and thicker construction to withstand major attacks. Rounded towers evolved out of the need to provide more visibility and stability. As the armies became more mobile and powerful, especially when gunpowder became a prominent weapon, the need to create and the effectiveness of a strong hold diminished. Castles in the 14th and 16th centuries were designed as lavish palaces that served as the living quarters of royalty and the wealthy.