In the year 1115, fortifications were erected at the site by Gosewijn I, Lord of Valkenburg. This original wooden keep survived until 1122 when it was destroyed under siege by Henry V, Holy Roman Emperor. The castle was rebuilt in the following centuries but was again destroyed in a siege, this time by Jan III, Duke of Brabant. The current ruins are those of the castle rebuilt in the 14th century.
The castle was blown up during the Franco-Dutch War, in 1672, by the army of King-Stadtholder Willem III to prevent it falling into French hands.
References:Visby Cathedral (also known as St. Mary’s Church) is the only survived medieval church in Visby. It was originally built for German merchants and inaugurated in 1225. Around the year 1350 the church was enlarged and converted into a basilica. The two-storey magazine was also added then above the nave as a warehouse for merchants.
Following the Reformation, the church was transformed into a parish church for the town of Visby. All other churches were abandoned. Shortly after the Reformation, in 1572, Gotland was made into its own Diocese, and the church designated its cathedral.
There is not much left of the original interior. The font is made of local red marble in the 13th century. The pulpit was made in Lübeck in 1684. There are 400 graves under the church floor.