A particularly muddy stretch of road through a swamp in Cornwall that served an important purpose in Béroul’s Tristan.
Isolde, being taken to a public trial in which she would be forced to deny any affair with Tristan, had to pass through Mal Pas. She arranged for Tristan, disguised as a leprous beggar, to be sitting by the side of the road there. When she arrived with her entourage, she fretted about crossing the swamp and ruining the hem of her skirt. She summoned the “leper” to piggy-back her over the pass. Then, at her trial, she was able to swear before God that no one except Mark and the “leper” had ever been “between her legs”.
Beroul injects a good deal of humor in the story by having the “leper” direct Mark’s advisors – and Tristan’s enemies – into the deepest, muddiest parts of the swamp.
Source
Tristan | Béroul, late 12th century