Claim: Pembroke Castle is a structure.

A castle -LRB- from castellum -RRB- is a type of fortified structure built in Europe and the Middle East during the Middle Ages by European nobility . Scholars debate the scope of the word castle , but usually consider it to be the private fortified residence of a lord or noble . This is distinct from a palace , which is not fortified ; from a fortress , which was not always a residence for nobility ; and from a fortified settlement , which was a public defence -- though there are many similarities among these types of construction . Usage of the term has varied over time and has been applied to structures as diverse as hill forts and country houses . Over the approximately 900 years that castles were built , they took on a great many forms with many different features , although some , such as curtain walls and arrowslits , were commonplace .   A European innovation , castles originated in the 9th and 10th centuries , after the fall of the Carolingian Empire resulted in its territory being divided among individual lords and princes . These nobles built castles to control 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 that were integral to life in the community , such as mills and fertile land .   Many castles were originally built from earth and timber , but had their defences replaced later by stone . Early castles often exploited natural defences , lacking features such as towers and arrowslits and relying on a central keep . In the late 12th and early 13th centuries , a scientific approach to castle defence emerged . This led to the proliferation of towers , with an emphasis on flanking fire . Many new castles were polygonal or relied on concentric defence -- several stages of defence within each other that could all function at the same time to maximise the castle 's firepower . These changes in defence have been attributed to a mixture of castle technology from the Crusades , such as concentric fortification , and inspiration from earlier defences , such as Roman forts . Not all the elements of castle architecture were military in nature , so that 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 .   Although gunpowder was introduced to Europe in the 14th century , it did not significantly affect castle building until the 15th century , when artillery became powerful enough to break through stone walls . While castles continued to be built well into the 16th century , new techniques to deal with improved cannon fire made them uncomfortable and undesirable places to live . As a result , true castles went into decline and were 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 .