The construction of defensive walls in Chełmno began in the second half of the 13th century. In the first quarter of the fourteenth century fortifications were raised. In the fifteenth and sixteenth century, the walls underwent further modernization as a result of which they were again raised, and in 1563 the battlements were walled up. Damages made during the Wars of Sweden were renewed in 1678. Walls were also repaired in the 19th century, but in the years 1860-1870, demolition of all gates except Grudziądz Gate, and a part of the walls south of it, were carried out.
The length of the perimeter walls was over 2,300 meters. The ring of fortifications was led along the edge of the upland and perfect natural defensive conditions were used. In places more easily accessible, that is from the east and west, there were moats filled with water. The defensive wall was made of brick in the monk bond on a foundation of glacial erratic boulders. The original battlement of the walls had arrowslits, later bricked up and an offset on the inside, on which there was a wooden platform communicated with the towers and gates. The city had 25-27 towers, presenting various types: open from the city, closed rectangular and circular located in the southern section of the walls. Access to the city was possible by the gates, situated at the outlets of the streets: Merseburg Gate, Grudziądz Gate, Water Gate, Franciscan Gate, Weavers Gate, Toruń Gate and Bridge Gate.
Chełmno, as one of the few Polish cities, can boast of an almost fully preserved circumference of the medieval defensive walls. It is currently 80% of their original length with 23 towers preserved. The most interesting of these are: Powder Tower where the archaeological section of the Chełmno Land Museum is located, Dominican and Virgin Towers, where the seat of the Knight’s brotherhood of Chełmno is situated. Until today, the Grudziądz Gate, located on the eastern side of the city, has been preserved, thanks to the sacral function it has performed since the 17th century and partly the Merseburg Gate within the monastery complex. In the north-western part of the city, at the post-Cistercian monastery, the so-called Mestwin Tower is located. It comes from the second half of 13 century and most likely is a part of the former Teutonic residence. At the same time, it is one of the few examples of a residential tower.