The Vikings had a stronghold at Aggersborg surrounded by an enormous rampart. Towering to the north of the rampart there is a church of Aggersborg, probably erected during the 12th century. An interesting illuminated inscription of runes can be seen on the walls of the nave and the northern chancel wall. The altarpiece dates back to 1598, but it wasn't placed in Aggersborg until 1934. The previous altarpiece can be seen on the northern wall of the nave. It pictures the founding of The Lord's Supper. There used to be family burial places behind the beautiful lattice.
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.