There are two ancient hill forts in Porvoo, so-called small and big one. There is burial ground in a small hill from the Roman Iron Age (0-400 AD). The items found in excavations reveal that Porvoo river has been a remarkable trading centre already in prehistoric times and local people has had connections to Estonia and Latvia.
The bigger hill fort is one of the largest in Finland. It was used for defensive purposes already in the Viking Age (800-900 AD), but the fortifications date from the late 14th century. Today remains of double walls and dry moat are visible and restored.
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.