Buelt

A region of South Wales now called Builth.

Nennius cites it as one of the wonders associated with Arthur: while Arthur was hunting the boar Troynt in the country, his dog, Cabal, left his footprint on a stone.

Arthur piled a heap of stones there as a monument to the event. If any stone was removed and carried away, it would vanish and reappear on the mound the next day.