In 1381, the teutonic grand master Winrych von Kniprode granted urban rights to a settlement. The shape of the town was adapted to the terrain conditions and began to be surrounded by defensive walls. During the Great War with the Teutonic Order in 1410, Polish troops occupied the town and the castle without a fight. After the Battle of Grunwald, king Władysław Jagiełło granted Nidzica to the prince of Masovia, however in September 1410, the Teutonic Knights regained the town. In 1444, Nidzica joined the anti-Teutonic Prussian Union, which in 1454 appealed to king Kazimierz Jagiellończyk with a request to join the Kingdom of Poland. In response, the Polish troops took over the town again without a fight. As a result of the Second Peace of Toruń, Nidzica remained in the territory of the Teutonic Order. Large wreaks, also for urban fortifications, were brought by Swedish wars in the 17th century. In 1664, the town was burned in a great fire. This contributed to the gradual fall of the fortifications and then their demolition.
The shape of the town fortifications was similar to the rectangle, from the north and west protected by the Wkra river. The wall was about 900 meters long and more than 5 meters high. It was strengthened with half towers, opened from the side of the town. In the corners of the wall there were more powerful, closed towers. Best strengthened was the eastern part of the circuit, in the middle of which, a 11-meter-long tower was erected. The entire eastern curtain was equipped with 9 towers and a second, lower, external defensive wall added at a later time. Two gates led to the town: from the north the German Gate, and from the south the Polish Gate. From north-east there was a so-called “Klasztorek” granary building. Within the town walls there was also the defensive church of St. Adalbert. The outer system of fortifications was provided by the river and moat.
From the town walls to this day, very few fragments have survived, mostly embedded in the walls of modern houses. The best preserved element is the so-called Klasztorek in the south-eastern part of the town. Originally, its eastern part served as a corner tower. Currently, it has been adapted for the branch of the State Archives. Also at Mickiewicza street are preserved relics of the tower.