Devil's Dyke is over 7 miles (11 km) long and is the largest of a series of ancient Cambridgeshire dykes. In some places the bank measures 9 metres (30 ft) high and 36.5 metres (120 ft) across. Its highest point is at Gallows Hill where it measures 10.5 metres (34 ft) from the bottom of the ditch to the top of the earth wall.
Wikipedia Entry
Devil's Dyke (Guardian)