The steep plateau of Saint-Blaise oppidum is accessible only from the south, therefore easy to defend, was inhabited from the Neolithic until the end of the 14th century with a long interruption during the High Roman Empire (from the 1st to the beginning of the 4th century AD). The excavations undertaken by Henri Rolland in 1935 and continued after his death, have brought to light eight archaeological layers.
There are today remains of Hellenistic rampart (2nd century BC), surmounted by the early Christian walls, a Christian necropolis, and foundations of 11th century church. The Chapelle St-Blaise is a 12th century Romanesque building, restored in the 13th century and whose facade was redone in 1608.
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.