St. Peter's Church have been probably built in two phases during the 12th century.The eastern part with chancel, transept and central tower were erected first during the late 1100's, while the nave and the present west tower were added later.
According the tradition the church was used as a bishop’s cathedral until 1130 when the bishop's seat was moved to Gamla Uppsala. The another legend believes the church has been a royal church. After a fire in the 1600s, the church has stood as a ruin.
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 LĂĽbeck in 1684. There are 400 graves under the church floor.