The Castello Svevo ('Swabian' or Hohenstaufen Castle) was originally built by the Saracens on the ruins of the ancient Rocca Brutia, around the year 1000. The castle was restored by Frederick II, Holy Roman Emperor, adding the octagonal tower to the original structure, in 1239. According to tradition, his son Henry lived in this castle, as a prisoner at his father's command. Louis III of Naples and Margaret of Savoy married in the castle and they both settled there in 1432.
All signs of the ancient Saracen structure have now disappeared. In the internal cloister, the modifications made by the Bourbons in order to convert it into a prison can also be seen. The entrance-hall is covered by ogival arches with engraved brackets. A wide corridor is dominated by some fleur-de-lis from the House of Anjou coat of arms. They are engraved on the ribbed Hohenstaufen arches.
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.