The walls of the ancient Fishermen's Chapel are reputed to date from the middle of the 6th century, but some authorities give a later date. It is however only a few monastic chapels survived the destruction of over fifty others at the hands of the Reformers in the 16th century. The material used in the chapel is the same as was used in the parish church: limpet shells crushed and dissolved with boiling sea-water. The stone roof was raised in the 14th century. The monks of that period evidently found the roof too low and squat for wall paintings. These were discovered in 1918. After a severe storm, colour was revealed on the ceiling and a picture of the 'Assumption' was seen, but in a damaged condition. But underneath the plaster was found another painting, 'The Annunciation', of about 1310-1315 A.D. At the foot of this painting are seen fourteen figures, supposedly members of an old Jersey family, the head of which had paid for this painting.The floor was restored to its earlier level in the 1980s to the medieval level, and the 'low, squat' aspect of the chapel which appears in early photographs is now gone, as the proper proportions can be seen.
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.