Visby was probably established the year 897. At that time big parts of Gotland were swamp areas. The downtown ascends from the coast-line terraced up against Klinten 40 meters above sea level.
  Visby's settlement is considered constructed after a regulated planning system with narrow streets. In the center of the current downtown, fresch water was in good supply. The source-tributary became an important reason for the development of Visby to a medieval large town. You can listen to the spring´s sound today from the cellar of St. Karin's ruined monastery.
  During the viking period Visby began to assume the caracter of a built-up area. As from the end of the 11th century Gotland dominated the lucrative long-distance trading with Russian products, directed towards Western Europe.
  The population of Visby increased with the Germans' immigration in the middle of the 12th century, as rumours about Gotlanders' accumulated wealth and success was widespread. Visby became a big transit town for merchants.
  It's hard to tell how many citizens that lived in this ultra modern town with lofty stone buildings and more churches than anywhere else in Sweden. About 3000 people live 'behind the walls' nowadays, estimations for the medieval period are about 6000.
  Visby got its first latrine system when the houses were built with combined privy and rubbish chute. Several latrine chambers were connected together and ended in the harbour.

Not mentioned in the text above is the Dome church with 3 towers, built by Germans in the end of the 12th century. It's the only church still in use.

  Churches: At The Cliff Terrace was since 1190 a German visitor church, as probably one Russian church in the quarter of "The monk". In the NE corner bishop Albert from Riga built a guest church dedicated to St Jakob, and during 1220 the Dominicans built their friary and the big church of St Nikolai. In 1240 the Order of the Germans in Visby probably raised the hospitality and the church of 'Helge And', while the Franciscan Order were residing above 'Stora Torget' [The big square] in 1233. St Per and St Clemens and St Olof became churches before 1200.
  The harbour entrance was defended by Kruttornet [Gun powder tower]. It connects with the sea wall which was built in the middle of the 13th century. All these buildings show the fast growth of Visby during the Medieval times.

  Visby enjoyed full membership in the Medieval trading organisation, the Hanseatic League (Hansa), but it wasn't the membership that gave rise to the grandeur of Visby. Merchants on Gotland had been traders before that with contacts around the Baltic Sea, also engaged in long-distance trading through Russian interior the long south-east way to the Christian Bysans. And it was in trading solidarity with the farmer-merchants on Gotland. When the merchants in Visby broke away from the Gotlandic union and joined the town-based union of Hansa, it probably led to the civil war of 1288. During the 14th century Visby lost its position as the biggest trading town for goods to Russia and the Baltic countries. In 1350 the Great Plague came to Gotland, and only 11 years later in 1361 the Danish king Valdemar Atterdag invided Gotland and Visby. It was in 1645 that Gotland once again became a part of Sweden.