An ancient linear earthwork runs intermittently from Naphill in Buckinghamshire to Dunstable in Bedfordshire. It is most easily visible at Pitstone Hill and near Great Hampden, especially the stretch running north-east from Redland End. It is thought perhaps to have served as a boundary marking the Iron Age limit of the territory of the Catuvellauni, and the gaps in it may once have been closed by forest land or fences and hedges long disappeared. The earthwork has been called Grim’s Ditch or Dyke since at least the 13th century.
These are by far the commonest names to have survived in connection with linear earthworks from the Middle Ages and earlier. There are Grim’s Ditches in Hertfordshire; in Middlesex; in Berkshire, and in other areas now in Oxfordshire, and also a Grim’s Bank running from Little Heath to near Padworth; also in Hampshire, Wiltshire and finally, Dorset.
The name ‘Grim’ is evidence in itself of ancient traditions concerning such structures, which appear to have been ascribed a supernatural origin. Coming from Old English grima, which can mean either ‘goblin, spectre’ or ‘mask’, it was perhaps used in England as a nickname for the god Woden, but in the Middle Ages was another name for the Devil. In some places, the name ‘Grim’ now alternates with that of the Devil in the names of ditches and dykes.
Though only rarely do legends still exist accounting for thee earthworks, the exception tht proves the rule comes from Hertfordshire, where one of the Grim’s Ditches is said to be the handiwork of the magician Sir Guy de Gravade of Tring Station. Possibly the Revd J. W. Burgess had this in mind when he observed in Records of Buckinghamshire (1858) tht the ditch owed its name both to the general superstition concerning the supernatural origins of earthworks and to a belief that only a magician could dig a trench so deep and long. Asserting that Grima was Saxon for a magician, he adds, ‘And with this clue, we may fairly interpret Grimsdyke as the Ditch of the Wizard.’
Whether or not local people connected Grim’s Ditch with wizards, they certainly had fantastic ideas of its size. The Revd Burgess noted that the country people commonly asserted that it ran round the world, as if Grim’s Ditch ‘like the Sea Serpent, drags its length along beneath the surface’. Many other traditions concerning the Ditch were also current in his time. He writes:
It is a weird or wizard spot, upon its bank nothing of good omen happens. I have been told in perfect good faith, by one who dwelt near it, that on Grimsdyke the unhappy Jane Shore perished, being starved to death by King Richard’s order, a baker also being put to death for his compassion in offering her a penny loaf… That fairies make fun, or make mischief, that ghosts and spectres have peculiar liberty on the soil of the Dyke, is the current belief of the country gossips.
A certain superstitious awe long remained attached to the earthwork. In 1910, it was recorded that at Bayman’s Green Wood there was once talk of filling up Grim’s Ditch which passes it, ‘but the people were afraid to do it’.