After 1525, Friesland became part of the kingdom of Charles V, who had a large fortress built at Stavoren harbour in order to keep the Frisian people under control. A blokhuis is an old Dutch term for a military stronghold with a strategic location to guard an entrance route, in this case Stavoren harbour. It stood here until around 1580. It was then gradually dismantled, and the stones incorporated in the city walls. During excavations in 1996, parts of the walls and towers were found, along with many cannonballs. A new representation of the stronghold has since been built on the location of the old foundations.
The choice fell upon an artwork of modern materials, including Corten steel, concrete and glass. The original foundations have been partly rendered visible to the public, and fitted with permanent exhibition windows displaying historic objects from Stavoren.