St Bilo's church is dedicated to a local saint named Bilo, or Beilo, daughter of Brychan. The dedication was recorded as early as the 13th century, but curiously, the church was known for many years as St Milburga's, after the daughter of a 7th century Mercian king and abbess of Wenlock. There must have been a Norman church here, for a reused lintel shows Norman carving motifs, but the building is almost entirely 14th century and later.
The chancel was rebuilt in 1710, and in the 19th century the west end of the church was blocked off and used as a schoolroom. In the south wall is a small window in Early English style, possibly a hermit, or leper window, and in the north wall is a blocked priest's door topped with a lintel carved with a traditional Norman diamond motif, suggesting an 11th-12th century date.
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.