The original church in the settlement of Sveti Tomaž, dedicated to Saint Thomas, was a Romanesque structure with a square nave and a rounded apse. The remains of this are still visible in the corner of the sanctuary. The surviving sanctuary is mostly Gothic, dating to around 1500.
The church was rebuilt a number of times, most extensively in 1848 when three layers of frescos were revealed, the oldest dating to the early 14th century, the second layer to around 1400, and the top layer to the early 16th century.
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.