The earliest history of Visby is uncertain, but it is known to have been a centre of merchandise around 900 AD. It was inhabited as early as the Stone Age, probably because of the access to fresh water and a natural harbour.
In the 12th century, Visby Cathedral, dedicated to Saint Mary, was constructed. It was reshaped in the 13th century to its current appearance, and was officially opened in 1225 by the bishop of the Swedish city of Link�ping. Several other churches were also constructed in the ensuing centuries. The city flourished, thanks to the German Hanseatic League.
The work on the ring wall was likely begun in the 12th century. Around 1300, it was rebuilt to reach its current height, acquiring the characteristic towers, although some towers were not constructed until the 15th century. The ring wall is still largely intact.
In 1361, Gotland was conquered by Valdemar IV of Denmark. 1800 Gotlanders were killed in battle in front of the city. Valdemar tore down part of the wall, set up three huge beer barrels and threatened to turn his men loose to pillage the town unless they were filled with silver and gold. The Visby city fathers fulfilled the demand, with churches stripped of their valuables. Valdemar added "King of Gotland" to his title list. His treatment of Visby, a member of the Hanseatic League, precipitated that League into war with Denmark; however, though Valdemar was forced into various concessions, he retained Visby as a Danish city.
In 1391, 1394 and 1398, it was taken and plundered by the Victual Brothers, pirates who sailed the Baltic Sea. An invading army ofTeutonic Knights conquered Gotland in 1398, destroyed Visby and expelled the Victual Brothers. In 1409 Grand Master Ulrich von Jungingen of the Teutonic Knights guaranteed peace with the Kalmar Union of Scandinavia by selling the island of Gotland to Queen Margaret of Denmark, Norway and Sweden.
In 1411, King Eric of Pomerania had the castle of Visborg
