Tarn Wadling lay in the heart of Inglewood Forest, the great hunting ground that stretched across the borderlands between England and Scotland, a landscape of oak and ash and deep green shadow that was already ancient when the Romans built their road to the north. The lake was small, perhaps five or six hundred yards across at its widest, a shallow pool fed by springs and rain, its waters dark with peat and rich with the carp that made it famous among medieval anglers. But its size was no measure of its reputation. In the thirteenth century, the writer Gervase of Tilbury recorded a lake in this area that he called Laikibrait, an anglicisation of the Old French lai ki brait, "the lake which cries." The name may have come from the methane that rose from the rotting vegetation on its bed, creating will-o-the-wisps that danced above the water at night, or from the strange sounds that echoed across its surface when the wind blew from the north. Whatever the cause, the tarn had a voice, and that voice made it a place of dread and wonder long before the Arthurian poets found it.

The lake entered the Matter of Britain through three Arthurian poems written in the fourteenth and fifteenth centuries, all of them set in the northern landscape of Inglewood and Carlisle. The earliest is The Avowing of Arthur, composed around 1375 to 1425, in which King Arthur, Sir Cei, Sir Baldwin, and Sir Gawain each swear a mighty oath. Gawain's vow is to keep watch by the tarn all night long, a task that tests his courage against whatever spirits the lake may send against him. The poem is a celebration of knightly virtue, and the tarn serves as the testing ground, the liminal space where the certainty of the mortal world meets the terror of the unknown. In the fifteenth-century poem The Awntyrs off Arthure at the Terne Wathelyne, the tarn becomes the stage for one of the most terrifying apparitions in Arthurian literature. King Arthur, Queen Guinevere, and their knights ride out to hunt in Inglewood Forest. The king gallops after a deer while the queen settles beside the waters of the tarn, guarded by Gawain. The sky darkens, a storm rises, and a hideous figure glides across the lake toward them. It is the ghost of Guinevere's mother, a rotting body covered in toads and serpents, with sunken glowing eyes, who speaks to her daughter from the torment of Purgatory. She warns Guinevere against the sins of lust and pride, prophesies the fall of Arthur and the destruction of the Round Table by the traitor Mordred, and begs for masses to be said for her soul. The apparition is composed of the very stuff of the tarn: clay, serpents, toads, black rot, and shadows, layered over a human skeleton, a "tarn-woman" whose body is made from the physical and aesthetic components of the lake itself.

The third poem, The Marriage of Sir Gawain, a ballad composed around 1500 and derived from the earlier romance The Wedding of Sir Gawain and Dame Ragnelle, places the tarn at the centre of the loathly lady story. King Arthur rides to "Tearne Wadling" where he meets the Baron of Tearne Wadling, a menacing knight who threatens the king's life and who is the brother of Dame Ragnelle, the hideous hag who knows the answer to the riddle that can save Arthur. Gawain must marry Ragnelle to win the answer, and the tarn is the place where the bargain is struck, the boundary between the courtly world of Camelot and the wild forest where enchanted women and vengeful barons hold sway. The baron's castle, Castle Hewen, was said to stand on a hill east of the tarn, and the name "Baron Wood" near the River Eden may be the last echo of his fortress in the modern landscape.

The tarn's literary fame was not merely a local affair. The fourteenth-century Gough Map, the earliest surviving map of Britain, marks Tarn Wadling alongside Lake Windermere as the only two bodies of water in that part of England, despite the Lake District with its many great lakes lying nearby. The poets who wrote of the tarn were likely patronised by the powerful Neville family, whose lands covered vast areas of the north and whose job it was to hold the border for the crown. By creating an Arthurian landscape in Cumbria, the poets gave southern lords a reason to imagine the north, and gave northern lords a connection to the Matter of Britain that rivalled the legends of the south. The poems were copied across England, from Lancashire to London, and the tarn's reputation spread far beyond the fields and woods where it actually lay.

In the nineteenth century, the tarn was drained for farming, and drained again in the 1940s. Today it is no more than a depression in the earth, a dip in the ground where cows graze and the wind blows across empty fields. Tarn Wadling Wood, a small patch of ancient woodland managed by the Woodland Trust, preserves the name, and the ruins of an old boathouse on what was once the eastern shore are the only physical reminder that a lake ever stood there. Yet the name endures, and the stories endure, and in the silence of the northern wind it is still possible to imagine the ghost of Guinevere's mother gliding across the water, the baron's challenge ringing through the trees, and Gawain keeping his lonely watch as the will-o-the-wisps dance above the crying lake.