Congenital iodine deficiency syndrome was especially common in areas of southern Europe around the Alps and was often described by ancient Roman writers and depicted by artists. The earliest Alpine mountain climbers sometimes came upon whole villages affected by it. The prevalence of the condition was described from a medical perspective by several travellers and physicians in the late 18th and early 19th centuries. At that time the cause was not known and it was often attributed to stagnant air in mountain valleys or bad water. The proportion of people affected varied markedly throughout southern Europe and even within very small areas it might be common in one valley and not another. The number of severely affected persons was always a minority, and most persons were only affected to the extent of having a goitre and some degree of reduced cognition and growth. The majority of such cases were still socially functional in their pastoral villages.