Around 1190, Walter Map included a tale about an otherwise unknown King Herla, allegedly ‘one of the most ancient British kings’, in his De Nugis Curialum. Herla entered a palace inside a hill at the invitation of a redbearded, goat-footed, hairy dwarf; he thought he spent a mere three days there, but was away 200 years. Returning to the human world, he and his men found that they crumbled to dust if they touched the ground, so they dared not dismount, and ‘this King Herla and his band still hold on their mad course, wandering eternally without stop or stay’—until they plunged into the Wye in the first year of Henry II's reign, and never appeared again.
Map goes on to describe ‘nocturnal companies and squadrons…engaged in endless wandering in an aimless round’, silent, and including people known to be dead; they had even been seen by day, but when pursued and challenged ‘rose up into the air and vanished suddenly’. This sinister company was known as ‘the household of Herlethingus’—probably an Anglo-Saxon phrase meaning ‘the troops of Herla’. Other medieval writers knew variants of this belief, and of this word. One tells of a great crowd of the tortured ghosts of sinners, some on foot and some on horseback, the ‘household of Herlechinus’; another talks of the Hell-bound ‘troops of Herlewin’. Although hunting is not involved, these spectral hosts are medieval forerunners of the Wild Hunt.
Westwood, 1985: 156–7, 251–3.