Devil's Dyke, Cambridgeshire

Devil's Dyke or Devil's Ditch is a linear earthen barrier, thought to be of Anglo-Saxon origin, in eastern Cambridgeshire and Suffolk. It runs for 11 kilometres (6.8 mi) in an almost straight line from Reach to Woodditton, with a 10-metre-high (33 ft) ditch and bank system facing southwestwards, blocking the open chalkland between the marshy fens to the north and the formerly wooded hills to the south.

Source: Wikipedia — Devil's Dyke, Cambridgeshire (CC BY-SA 4.0)