Windsor Palace is the world's largest and oldest continuously inhabited castle. occupying over 484.000 square feet, it is over 240 times the size of an average house. william the conqueror built the first castle on the grounds between 107o and 1086,but the castle that exists today was largely built by Edward of Windsor in 1350. Edward of windsor authorized the construction of a new keep, a large chapel, and new fortifications. From a distance, the castle appears dominated by a massive round tower in its center.