The main purpose of castles was to protect the people who lived there from invasions. They were also a status symbol to show other people how important a family was. Many ancient castles still stand in Europe today, and some of them have been home to the same family for many generations.

Castles were primarily developed in Europe during the 9th and 10th centuries as fortified residences for royalty and nobility following the collapse of the Carolingian Empire. The initial "Motte-and-Bailey" designs were built to provide local protection against Viking, Magyar, and Saracen raids during a period of extreme political instability. Beyond simple defense, castles served three main functions: they were military strongholds used to control territory, administrative centers from which a lord could govern his lands, and symbols of power that asserted the owner's status over the local peasantry. As siege technology advanced, castles evolved from simple wooden structures into the massive stone fortresses with moats, drawbridges, and keep-towers that we recognize today. By the 15th century, the advent of gunpowder and heavy cannons made traditional high stone walls vulnerable, leading to the transition from defensive fortresses to the more comfortable, unfortified "chateaus" and manor houses of the Renaissance.