In the 15th-16th century the settlement of Keila consisted some tens of buildings and a hundred people formed around the church. At the same time the Livonian Order built a small fort south-east of the church on Jõepark. During the Livonian War of 1558-1583 the settlement was destroyed.Further hampered by the plague and starvation in 1601-1602 the population declination reduced the community to a small church village. Ruins of the fort were first excavated in 1976 with continued finds up to 2007.
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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.