Grim's Ditch (Harrow)

From the longer Wikipedia page

Grim's Ditch or Grim's Dyke or Grimes Dike is an earthwork in the London Borough of Harrow (before 1965 in Middlesex) and lends its name to the gentle escarpment it crowns, marking Hertfordshire's border. It extended east-west about 3 miles (4.8 km) from the edge of Stanmore where an elevated neighbourhood of London, Stanmore Hill, adjoins Bushey Heath to the far north of Pinner Green. Today the remaining earthworks start mid-way at Harrow Weald Common.[1] It takes its name from the prehistoric earthwork which is one of seven Grim's Ditches, a few of which have two or three rows, in central southern England.