The extraordinary career of the historical Geoffrey de Mandeville inspired many strange traditions concerning him both in the Middle Ages and long after. There are conflicting tales of how he met his end, whether shot in the head by an arrow and then hung from a tree in London, or down a well here at the overgrown motte-and-bailey of South Mimms Castle, in Mymmshall Wood, north-west of Potters Bar.
Hertfordshire tradition says that Sir Geoffrey, being hunted down for one of his crimes, hid from his pursuers in a hollow tree. He could not escape divine retribution, however, and this tree immediately sank into the castle well, where he perished. His ghost is said to walk his former domains from South Mimms to East Barnet every six years at Christmas, dressed in full armour, with a red cloak, and accompanied by a phantom dog (see WALDEN ABBEY, Essex).
South Mimms Castle itself was probably built by Geoffrey, around 1140–2. By the time the sixteenth-century topographer William Camden was writing his Britannia, it was already in ruins. Tradition, however, says that, in its heyday, it had gates so huge that they could be heard closing as far away as Winchmore Hill.
W.B. Gerish does not mention the legend in The Folk-Lore of Hertfordshire, his useful checklist of traditions current in 1911, and indeed South Mimms Castle was only rediscovered in 1918. The story may therefore have been adapted from the pre-existing one concerning Camlet Moated Site, Enfield, on the north side of what is now Trent Park, where Geoffrey’s treasure is said to be hidden in an ancient well. That being said, both versions are now established.