St. Olof's Church was originally built around the year 1100 and it consisted of a main tower, chancel and nave. It was later extended, but the construction was probably interrupted when archbishop’s seat was moved to Gamla Uppsala in the 12th century.
St. Olof's church has been influenced by the Nidaros Cathedral in Norway, while the small tapering windows have an Anglo-Saxon style. The church is dedicated to the Norwegian viking Olaf Tryggvasson, king between 995-1000.
It is not certain by whom the church was built. Most probably it was authored by the Benedictines or local trade guild. Archaelogical excavations have revealed remains under the church, which are thought to have belonged to an even older stone church. It may have been one of the first built in Sweden.
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.