The Visby city wall is a medival defensive wall surrounding the Swedish town of Visby on the island of Gotland As the strongest, most extensive and best preserved medieval city wall in Scandinavia.

Built in two stages during the 13th and 14th century, approximately 3.44 km (2.14 mi) of its original 3.6 km (2.2 mi) still stands. Of the 29 large and 22 smaller towers, 27 large and 9 small remain. A number of houses that predate the wall were incorporated within it during one of the two phases of construction. During the 18th century, fortifications were added to the wall in several places and some of the towers rebuilt to accommodate cannons.

https://en.wikipedia.org/wiki/Visby_city_wall