Grim's Ditch is a series of linear earthwork in the Chilterns (southeast England). A complete outline cannot be identified but separate sections exist over a 30-kilometre (19 mi) span between Bradenham, Buckinghamshire, Berkhamsted, Hertfordshire and as far as Pitstone and Ivinghoe Buckinghamshire. Pottery shards have been unearthed in excavations during the 1970s and 1980s suggesting that its origin may have been during the Iron Age and was believed to have been during a period when the landscape was clearer of scrub and the dense woodland as today as the straighter sections would have required clear lines of sight. The first mention of Grim's Ditch was a grant of 1170–90 in the Missenden Cartulary referring to it as Grimesdic. The Anglo Saxons commonly named features of unexplained or mysterious origin Grim. The word derives from the Norse word grimr meaning devil and a nickname for Odin or Wodin the God of War and Magic.