It is believed that Saint Domangard or Donard founded a monastery in Maghera in the early christian period, c. 500 AD. He lived as a hermit on Slieve Donard, a nearby mountain that is named after him. There are no antiquities remaining from the early foundation but excavations in 1965 produced evidence of occupation around the tower during the Early Christian period. The medieval church situated behind the more modern church probably dates to the 12th century. It is much harder to date the round tower as there are no features such as windows or doors that normally help in dating round towers.
The tower, which is built from rough uncoursed granite field-stones similar to the tower at Castledermot, is believed to have fallen in the 18th century as a result of storm damage. All we see today is a 5.4 metre high stump with a large breech on the eastern side of the tower. This may represent the position of the doorway, suggesting a rather low entrance. The diameter of the tower at base level is 4.85 metres. The stones used in the building of the tower suggest a 10th century date but is not definite proof.
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.