The Abbey of Saint-Gildas is dedicated to St. Gildas (c. 500–570) who was a British historian and cleric. He is one of the best-documented figures of the Christian church in the British Isles during this period. According a legend Gildas established the abbey, but there are no written evidences. Buildings were destroyed by Norman raids in the 10th century.
The first known record dates from 1008 when the abbey was restored by the order of Geoffrey I of Bretagne. The new inauguration was held in 1032. The heyday of Saint-Gildas Abbey was in the 11th-14th centuries. During the Hundred Years' War most of the archives were destroyed. The monastery started to decay in the 16th century. The nave of the church collapsed in 1668 when a lightning hit it.
the next restoration took place in the late 1600s. The abbey church was moved as a parish church during the Great Revolution in 1796.
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.