Some Iron Age hillforts were also incorporated into medieval frontier earthworks. For example Offa's Dyke, a linear earthwork generally dated to the 9th century CE, makes use of the west and south-west ramparts of Llanymynech hillfort.[19] Similarly the hillfort at Old Oswestry was incorporated into the early medieval Wat's Dyke.[20] The Wansdyke was a new linear earthwork connected to the existing hillfort at Maes Knoll, which defined the Celtic-Saxon border in south-west England during the period 577–652 CE.