Early Anglo-Saxon settlements rose in Northchurch and Berkhamsted. In the Medieval period, the Bulbourne powered two watermills in Berkhamsted (Upper and Lower - recorded in 1086) and another in Bourne End. It also fed the three moats of the large Norman (Motte and Bailey) Berkhamsted Castle, that stands close to the center of the town. The river created a marsh environment (at times referred to as an 'unhealthy swamp') in the center of the valley, which added to the defenses of the castle.