For William the Conqueror in 1066, Dover was a strategic necessity for the survival and success of the Norman Conquest. Located at the narrowest point of the English Channel, Dover was the "Key to England." After his victory at the Battle of Hastings, William immediately marched on Dover to secure the port, as it was the primary lifeline for reinforcements and supplies from Normandy. If the English had held Dover, they could have cut off William’s retreat or blocked his communication with the continent. William of Poitiers, a contemporary chronicler, noted that the town was considered "impregnable," but the inhabitants surrendered out of fear. Upon capturing it, William spent eight days adding new fortifications—likely a timber motte-and-bailey castle—around the existing Saxon church. Securing Dover allowed William to safely advance toward London, knowing his rear was protected. The town's importance was so great that its valuation in the Domesday Book (1086) skyrocketed from £18 to £40, reflecting the massive revitalisation and military investment William poured into the port.