A royal castle site on Visingso where Erik Knutsson died in 1216.
Nas Castle was a Swedish royal fortress on the island of Visingsö in Lake Vättern, serving as an important administrative residence for medieval Swedish kings. Erik Knutsson died there in 1216, leaving a young heir and prolonging Swedish dynastic instability.
Visingsö and its castle remained a Swedish royal center through the thirteenth century before declining in importance as Stockholm grew. Nas Castle's connection to the Erik-Sverker dynastic conflict makes it a site of the contested Swedish succession that characterized the period.