Tŷ unnos (plural: Tai unnos) (One night house), is an old Welsh tradition which has parallels in other folk traditions in other areas of the British Isles. It was believed by some, that if a person could build a house on common land in one night, that the land then belonged to them as a freehold. There are other variations on this tradition: that the test was to have a fire burning in the hearth by the following morning; and that the squatter could then extend the land around by the distance they could throw an axe from the four corners of the house.