Medieval castles, emerging around the 9th century, were initially built as wooden motte-and-bailey structures in response to the fragmentation and instability of feudal Europe after the Carolingian Empire's decline. These early castles, featuring a keep on a raised earth mound (motte) and an enclosed courtyard (bailey), served as rapid, easily constructed defenses but were vulnerable to fire and weather. The 11th century brought a transition to stone construction, offering greater durability and more sophisticated defensive capabilities. This shift was especially pronounced after the Norman Conquest of England in 1066, as William the Conqueror established numerous stone castles to solidify control. With the advent of stone, castles began incorporating complex defensive features: high curtain walls, fortified gatehouses, moats, and imposing keeps.

As castles developed in structure and purpose, they became symbols of noble authority as well as defensive strongholds. By the 13th century, designs evolved into concentric castles, layered with multiple rings of defenses to withstand prolonged sieges. Inside, the spaces served varied functions that reflected the growing social importance of castles. Great halls became the administrative and social heart, where lords held court, banquets, and meetings. Private chambers provided more comfort for the lord's family and high-ranking guests, often featuring fireplaces, glass windows, and decorative elements that underscored their wealth and status. The castle chapel highlighted the vital role of religion, offering a space for worship within the castle. Kitchens and storerooms supplied the means to sustain inhabitants during peacetime and under siege, reflecting the castle’s role as a self-sustaining environment.

Medieval warfare in the age of castles heavily relied on siege tactics. Attackers employed strategies like blockades to cut off supplies, siege towers to breach walls, mining to destabilize foundations, and catapults to hurl stones or flaming projectiles. In response, castle defenders developed countermeasures: reinforced walls, thickened gates, and innovations like murder holes, where rocks, boiling oil, or other deterrents could be dropped on invaders. Moats provided an additional defensive perimeter, forcing attackers to expose themselves as they attempted to cross.

Beyond their military function, castles also played crucial roles in the economic and social landscapes. They were often administrative centers, where lords conducted judicial and financial affairs, reinforcing their control over the surrounding lands and vassals. Castles served as local economic hubs, supporting blacksmiths, masons, carpenters, and other artisans who maintained the structure and its defenses. Marketplaces commonly developed around castles, encouraging trade and providing income to the surrounding villages, which, in turn, supported the local feudal economy. These economic activities made castles focal points of regional trade.

Socially, castles embodied the feudal hierarchy. The lord’s family resided in the central keep, the symbolic and literal seat of authority, while soldiers, servants, and craftsmen occupied other areas, each role vital to the castle’s operation. This hierarchical arrangement mirrored and reinforced the broader social order of medieval Europe, where status dictated one’s responsibilities and privileges within the feudal system.

By the 15th century, advancements in military technology, particularly gunpowder and artillery, began to make traditional castle defenses less effective. Centralized monarchies further reduced the need for individual lords to maintain private fortified structures. Consequently, many castles transitioned to palatial residences, focusing on luxury and aesthetics over defense. This shift gave rise to the Renaissance châteaux and manor houses, which retained the prestige of the castle but not its military aspects.