Eskilstuna's history dates back to medieval times when an English monk named Saint Eskil established a base called "Tuna" and served as the bishop of the southern coast of Lake Mälaren. Saint Eskil was later killed by pagan Vikings for trying to convert them to Christianity. The monastery founded by Saint Eskil was eventually destroyed during the Protestant Reformation and replaced with Eskilstuna House, the royal castle. Eskilstuna was granted city privileges in 1659 and grew significantly during the Industrial Revolution as it became a major center of steel production in Sweden, earning its nickname "The City of Steel."