Visborg (Wisborg) refers to a fortress in the town of Visby on the Swedish island of Gotland. There was no one fortress called "Visborg", rather it refers to successive fortresses built in Visby (Borg in Old Norse means fortress or castle). Though Visborg is usually a reference to the castle built here by Erik of Pomerania History Duke Erik Magnusson appears to be the first to construct a fortress in the south-west corner of Visby in the year 1310 as part of a struggle between his brothers fo… (More on Visborg)