Medieval Castle Interior

Category: File - :Alcazar de Segovia.JPG|thumb|right|300px|alt=A castle high on a rocky peninsular above a plain. It is dominated by a tall rectangular tower rising above a main building with steep slate roof. The walls are pink, and covered with a sculptural pattern. There is a variety of turrets and details.|Alcázar of Segovia in Spain

Category: File - :Castle Bodiam1 cz.jpg|thumb|300px|alt=A castle of square plan surrounded by a water-filled moat. It has round corner towers and a forbidding appearance.|Bodiam Castle in England

A castle (from Latin castellum) is a defensive structure associated with the Middle Ages. Scholarly debate surrounds the term's precise meaning, but a castle is usually considered to be the "private fortified residence" of a lord or noble. This is distinct from a fortress, which was not a home, or a fortified town, which was a public defence. Despite the definition used by historians, the term castle has been popularly used to describe structures as diverse as hill forts and country houses; castles are found in Europe and the Middle East. Over the approximately 900 years that castles were built they took on a great many forms with many different features; some, such as the curtain wall and arrowslits, were common in castle architecture.

A European innovation, castles originated in the 9th and 10th centuries when the fall of the Carolingian Empire led to the division of the empire's territory among individual lords and princes. Castles controlled the area immediately surrounding them, and were both offensive and defensive structures; they provided a base from which raids could be launched as well as protection from enemies. Although their military origins are often emphasised in castle studies, the structures also served as centres of administration and symbols of power. Urban castles were used to control the local populace and important travel routes, and rural castles were often situated near features in the landscape that were integral to life in the community, such as mills.

Many castles were originally built from earth and timber, but had their defences replaced later by stone. In the late 12th and early 13th centuries, a scientific approach to castle defence emerged. Towers proliferated, with an emphasis on flanking fire, and many new castles were polygonal, while previously they had exploited natural defences and were curvilinear, or relied on concentric defence ? several stages of defence within each other that could all function at the same time, thereby maximising the castle's firepower. The origin of these changes in defence has been attributed to a mixture of influence from the Crusades ? where castle technology was advanced such as the development of concentric fortification ? and drawing on earlier defences such as Roman forts for inspiration. Not all the elements of castle architecture were military in nature, and devices such as moats evolved from their original purpose of defence into symbols of power. Some grand castles had long winding approaches intended to impress and dominate their landscape.

Gunpowder, introduced to Europe in the 14th century, did not have an immediate impact on castle building. Castles do not show adaptation to resist bombardment by cannons until the 15th century, when artillery became powerful enough to break down walls. Although castles were built across Europe well into the 16th century, new techniques to deal with improved cannon eventually led to them becoming uncomfortable and undesirable places to live, and so true castles went into decline, replaced by artillery forts with no role in civil administration, and country houses that were indefensible. From the 18th century onwards, there was a renewed interest in castles with the construction of mock castles, part of a romantic revival of Gothic architecture, but they had no military purpose.