Visborg

Duke Eric (son of King Magnus III of Sweden) appears to be the first to construct a fortress in the southwest corner of Visby in 1310 as part of a struggle between his brothers for control over the kingdoms of Sweden and Norway as well as Danish claims on Gotland; this brings Gotland under Norwegian control.

In 1375, King Valdemar of Denmark dies and Margaret ensures that her and Haakon's infant son, Olaf (Olav) is named heir to the throne.

Konrad von Jungingen, the Grand Master of the Order, takes the Island in 1398 and destroys Visby.

This began a long period of warfare between the kings of Denmark and Sweden over who would once again rule over the three kingdoms of the Kalmar Union.

In 1448, Charles launched an invasion of the island and was able to secure all but Visby because of the fortifications at Visborg, still inhabited by the deposed King Eric.

Eric made a deal with Christian I in 1448, because they were family, in which he agreed to cede Gotland to the Danes and renounce his claims to the throne in return for safe passage to Pomerania.

Christian agreed and in 1449, a Danish army reinforced the defenses of Visborg by sneaking in under cover of darkness.

Despite numerous challenges, Denmark retained continuous rule of the island until a peace treaty[further explanation needed] signed in 1645 granted it to Sweden for 30 years.

Prince Oscar of Sweden, Duke of Gotland and second in line to the Swedish throne, married without his father's permission, thereby relinquishing his right to succession and royal titles.

On 2 February 1892 he was made the first Count of Wisborg by his mother's (Sophia of Nassau) brother Adolphe, Grand Duke of Luxembourg with reference to the old fortress of his former dukedom.