St Illtyd's Church is located at the site of the oldest college in the United Kingdom, Cor Tewdws, which was founded c. 395 AD in honour of the Roman Emperor Theodosius I. It was refounded by St. Illtud c. 508 AD, from whom it derives its name. The current church building was built in the 11th century by the Normans, with portions being rebuilt in the 13th and 15th centuries. The church building is one of the oldest and best-known parish churches in Wales. It is a grade I listed building, or building of exceptional interest, and has been called both the 'Westminster Abbey of Wales' for its unique collection of carved stones and effigies, and 'the most beautiful church in Wales.'
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.