Marmiroi church is mentioned in historical records for the first time in 1307. Since it has no narthex, and because of other similarities to other similar churches in Bulgaria and former Yugoslavia, it is thought to have been built in the 12th or 13th century AD, although some researchers have put its construction period in the 10th century. The most accredited hypothesis is that it was dedicated to Saint Mary.
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.