 An early reference to the practice occurs in “The Dream of Rhonabwy”, a Welsh story from the Mabinogion, a remarkable collection of medieval literature.Written before the 14th century, The Dream of Rhonabwy refers to the mid-12th century in Powys.The floor of the old black house of Heilyn Goch is described as being covered in the urine and dung of cows together with branches of holly whose tips had been eaten by the cattle.