Salt travelled throughout Europe from Antiquity to the early 20th century. In the Alps where it was rare, it was an essential commodity. It was used to preserve food and its iodine content kept people and livestock healthy. Salt was an expensive and sacred material, used in medical and veterinary practices, magic rituals and prophylactic exorcism. The Old Testament decrees that any food offering must contain salt, particularly when it accompanies the crossing of a threshold. In some regions, sharing salt, along with bread and water, cements alliances. Even today, this custom is surrounded by many cautions.