In 963 AD Emperor Otto I granted to Adalberto Bishop of Luni ownership of the castrum Sarzanae, a fortified village where today the fortress of Sarzanello is located.
Cittadella or Fortezza Firmafede was the first fortress in the city built in 1249. It was destroyed by the Firenze army led by Lorenzo de Medici in 1487 and rebuilt after the war by Medici. It was reconquered by Genoa Republic in 1494.
Today the massive square form building is used as a venue for culture events and exhibitions.
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.