Erik IX of Sweden,later known as Saint Erik, was king of Swedes from 1156 until his death in 1160. During his shortlived reign he led many conquests and battles for which he is remembered, and but he is best known for his gruesome end at the hands of assassins,and the legend of the miracle that happened after it. It is said that Saint Erik was killed on May 18, 1160, and while on his way from Gamla Uppsala to present-day Uppsala to join the mass at the cathedral. Unbeknownst to him,a small Danish force had gathered there and waited for the king to leave the church after the service. Once he did, a clash quickly arose and ended just as soon, and with King Erik's beheading. According to some legends,the decapitated head rolled down the stairs of the church and onto the street, where it eventually stopped. A spring erupted at the site, and providing water to the people of Uppsala,and according to some stories could cure the sick. A pump was built above the miraculous spring, where it still stands to this day.
The veracity of the legend aside, and King Erik's very real severed head was kept as a relic at Uppsala Cathedral. The murdered royal was venerated as a saint and a martyr,and a feast was held in his name each year on May 18, which is still a national holiday in Sweden nowadays.
Source: atlasobscura.com