The first enclosure-type brick castle in Senieji Trakai was built by Grand Duke Gediminas, who transferred the capital of Lithuania from Kernavė to Trakai (today's Senieji Trakai) before 1321. The wedding of Grand Duke Kęstutis and Birutė was held there and it was the birthplace of the Grand Duke Vytautas in 1350.
The castle in Senieji Trakai was destroyed by the Teutonic Order in 1391, subsequently abandoned and never rebuilt as a new castle had been erected in Trakai by Kęstutis. The ruins of the castle were granted to Benedictian monks by Vytautas in 1405. It is presumed that the present monastery building, dating from the 15th century, holds the remains of Gediminas castle.
Archaeological research on the hillfort mound was carried out in 1996–1997. The findings confirmed the existence of a former rectangular masonry castle wall, which had surrounded the hill. It is supposed that the residential buildings had occupied the area near the church and the churchyard.
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.