The Normans were the first group of people to build castles in England, although the Romans before them had built forts that the Normans then expanded and improved. Initially, castles were built out of wood, but eventually, people made castles from stone because they were stronger and lasted longer.

The concept of the "castle"—a private fortified residence—is primarily credited to the Normans in the 9th and 10th centuries. While ancient civilizations built massive walled cities and forts, the specific architectural form of the castle emerged in Western Europe after the fall of the Carolingian Empire. These early structures were known as Motte-and-Bailey castles, consisting of a wooden keep on a raised earth mound (the motte) and an enclosed courtyard (the bailey). Following the Norman Conquest of England in 1066, William the Conqueror initiated a massive castle-building campaign to consolidate his power, including the construction of the White Tower at the Tower of London. These structures evolved from wood to stone over the subsequent centuries, but it was the Norman innovations in fortification and feudal lordship that truly defined the birth of the medieval castle as we recognize it today.