The Co-Cathedral of the Assumption of Mary was built in 1169 as a Romanesque basilica of a single nave on the foundations of a pagan temple of the fourth and fifth centuries, whose remains are still visible at the back of the sanctuary at about 1.5 meters deep. The façade and the south side of the cathedral, in the middle of the eighteenth century was decorated with Romanesque arches and brick niches. In the same period the church was expanded with the addition of two side aisles, altars and other works of art. During World War II the cathedral was severely damaged. The current appearance of the building is the result of the restoration executed between 1949 and 1950.
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.