Square Keep Castles: When, Why, and How They Shaped Medieval Defense

When: 11th–13th centuries. The Normans introduced them to England after 1066; they spread across Europe.

Why: As fortified lordly residences and military strongpoints. Thick stone walls (3–4 m), corner towers, and elevated entrances resisted siege engines. The square plan simplified construction and gave defenders clear fields of fire on all sides.

Evolution: Vulnerable to undermining at corners; later replaced by round towers, concentric walls, and gatehouse complexes. Yet many survive as iconic symbols of Norman power (e.g., Tower of London, Rochester, Dover).