The City wall of Visby (Swedish: Visby ringmur) is an old medieval defensive wall surrounding the city. The building of ringwall was probably started in the 13th century. Around 1280 it was rebuilt to reach its current height, along with the addition of its characteristic towers (although some towers were not constructed until the 15th century) It is part of the UNESCO World Heritage Site in Visby. The war in 1288 between the citizens of Visby and the Danish army gave the citizens of Visby a reason to continue the work with the wall. All together the city wall became 3.4 km, and it was finished in the beginning of the 14th century. At the time, the wall contained 29 towers, 27 of which are remaining today.
During the 1361 Battle of Visby, the main battle was fought within 300 meters of the North Gate of Visby (shown on the right). The peasant forces were ultimately unsuccessful, however, resulting in the citizens of Visby surrendering to the Danish forces.
References:Château de Niort is a medieval castle in the French town of Niort. It consists of two square towers, linked by a 15th-century building and dominates the Sèvre Niortaise valley.
The two donjons are the only remaining part of the castle. The castle was started by Henry II Plantagenet in the 12th century and completed by Richard the Lionheart. It was defended by a rectangular curtain wall and was damaged during the Wars of Religion. In the 18th century, the castle served as a prison.
The present keeps were the central point of a massive fortress. The southern keep is 28m tall, reinforced with turrets. The northern tower is slightly shorter at 23m. Both are flanked with circular turrets at the corners as well as semicircular buttresses. Each of the towers has a spiral staircase serving the upper floors. The Romanesque architecture is of a high quality with the dressed stones closely jointed.