The credit for building the first "true" castles in Europe belongs to the Normans in the late 10th and early 11th centuries. These early structures were known as Motte-and-Bailey castles. A "Motte" was a large, man-made earthen mound topped with a wooden keep or tower, while the "Bailey" was an enclosed courtyard at the base, protected by a wooden palisade and a ditch. While various cultures had built hillforts and walled cities for millennia, the Norman castle was a distinct innovation: a private, fortified residence designed for a local lord to control a specific territory and its population. This style of fortification became the architectural "weapon" that allowed William the Conqueror to successfully pacify and control England after the Battle of Hastings in 1066. Within a few decades, the Normans began replacing these wooden structures with massive stone keeps, such as the White Tower at the Tower of London, marking the transition into the iconic age of medieval stone castles that still dominate the European landscape today.