While many castles dot the landscape, The Tower of London is widely considered the most iconic and historically significant of all English fortresses. Founded by William the Conqueror in 1066 as part of the Norman Conquest, its central "White Tower" has served as a royal palace, a notorious prison, an armory, a treasury, and the home of the Crown Jewels for nearly a thousand years. Its distinctive square silhouette and its location on the banks of the River Thames make it the definitive symbol of royal power and English history. However, from a purely "military" and "fortress" perspective, Dover Castle is often called the "Key to England." Perched on the iconic White Cliffs, it has protected the English coast from invasion for centuries, from the Roman era through the Napoleonic Wars and even World War II, where its tunnels served as a command center for the Dunkirk evacuation. While Windsor Castle is the most famous royal residence, the Tower of London remains the most "iconic" in the public imagination as the quintessential medieval fortress that has witnessed every major chapter of the nation's storied past.