Castles could serve as a centre for local government, administration and justice. They were also used by powerful lords to display their wealth and power through lavish architectural styles and decoration. Castles were not only built and used by the crown.

Medieval castles fundamentally transformed European society by serving as both military strongholds and centers of political and economic administration. Strategically, they acted as a "force multiplier," allowing a small garrison of soldiers to defend a vast territory and suppress local rebellions. Economically, castles often functioned as toll collection points along major trade routes and rivers; merchants were compelled to pay for passage under the "protection" of the local lord. Socially, they were towering symbols of royal authority and feudal control, often striking fear into the surrounding peasantry. Castles catalyzed the growth of towns, as merchants and artisans settled near the walls for safety, creating "boroughs." While they were a massive economic burden to build and maintain, their presence defined the power dynamics of the Middle Ages, shifting the focus of warfare from open-field battles to prolonged sieges and cementing the "manorial" system of justice.