Around 1,700 ruins of Medieval salt production huts have been identified on the island of Læsø. It is shown that present-day settings of hypersaline groundwater accumulations are comparable to the palaeo-settings of the Medieval salt production
and that up to 135 production huts were simultaneously active during more than 400 years from the production began around 1150–1200 until the industry culminated around 1585 and completely ceased only a few decades later. The growth and decline in number
of active production huts was not only caused by shortage of fuel as hitherto believed, but more importantly caused by climatic cooling and lack of hypersaline water.