King Hans's 1504 attack on Olsborg Castle

Nils Ravaldsson commissioned the construction of Olsborg Castle in 1502 as a response to a recent Norwegian-Swedish rebel attack on Viken. Located on a steep cliff, the site might have previously been an early hill fort. Although a one-year ceasefire with rebels was signed in May 1504, the peace proved fleeting. The forces of Scandinavian monarch King Hans attacked during a Christmas party in 1504, destroying most of the castle.

Following the turmoil from the dethronement of the Danish king Christian II, the Swedes seized the area and reconstructed the fortifications. Between 1523 and 1525, the nobles Lars Siggesson and Ture Jönsson used the castle to administer northern Bohuslän. They improved the defenses in 1526, but Norwegian forces destroyed both the castle and the nearby Karlsborg Castle in December 1531 during Christian II's attempt to retake his throne.

During the 1560s and 1570s, Swedish monarchs Eric XIV and Johan III both attempted to rebuild the castle, but these efforts were unsuccessful and it remained in ruins. The remains were still visible in the early 20th century when Swedish archaeologist Wilhelm Berg excavated the site. Berg served as the secretary of the Gothenburg and Bohuslän Antiquities Association and had previously excavated the Ragnhildsholmen fortification.

Sources: Wikipedia, OpenStreetMap, Wikidata, Wikimedia Commons