Constantina Castle was dates back to the Moorish period, when it defended the north-south road towards Seville. It was conquered by Christians in 1274 and by the privilege of King Alfonso X in 1253, it passed to the Alfoz of Seville. In 1810, it was used as a fortified point during the period of the French invasion of the town.
Today the castle of Constantina consists of a polygonal enclosure of about ninety metres in diameter, which has an external defence in the form of a barbican, of which there are sufficient remains to affirm that it completely surrounded the enclosure. Most of this area has been preserved, and two of the seven towers that flanked it are still complete, containing magnificently built circular vaulted chambers.
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.