Isegran is the first place in Fredrikstad mentioned in history. The Earl of Borgarsyssel, Alv Erlingsson, also called MindreAlv, had a small fortress on Isegran in the late 1200s. In the 1670s, the island was fortified with a large battery platform, Isegran tower, and later a small fort was built to protect the river. Until 1685 Isegran was the royal shipyard for the danish-norwegian fleet and during the Great Northern War, the island was the naval base for Peter Wessel Tordenskiold. The historic island can be reached via the Kråkerøy bridge or with the city ferry.
References:The Gravensteen is a castle in Ghent originating from the Middle Ages. The name means 'castle of the counts' in Dutch. Arnulf I (918–965), Count of Flanders, was the first to fortify this place, building a medieval bastion on this high sand dune, naturally protected by the river Leie and its marshy banks. This bastion consisted of a central wooden building and several surrounding buildings, also in wood.
In the early 11th century, the wooden building was replaced by a stone residence, consisting of three large halls that made up three storeys, connected by a stone stairwell. The monumental stone staircase, the light openings, the fireplaces built into the walls and the latrines were signs of considerable luxury and comfort in those days. There was probably also a tower.