Château d'Ailly was first mentioned in 1050 when Robert d'Ailly built a manor surrounded with walls, moat and mill. The near St. Gerbold's Church was also built then. In 1431 english King Henry VI gave the land property of Ailly to his uncle. Back in French possession, the manor belonged to the Courseulles and De Saint Laurens families until it was acquired by d'Aubert de Caudémone in the 17th century. Charles d'aubert d'Ailly, a Knight of Malta, transformed the château in 1721 to the current appearance.
The archaeological project in 1832 unearthed the nine famous d'Ailly helmets, which were well-preserved helmets dated back to the end of Bronze Age.
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.