For quite a while the walls of 1125 had beeen too small. As long as anyone could remember, a few large farms lay outside the walls, including the farm buildings of the Reichhof transferred from the castle area. The encircled settlement of the Order of St. John (the origins of the Marienkirche) also lay outside the walls, and a road leading to it (Beeckstrasse) would have been built. Outside the walls a few buildings had arisen in the area of the current Alt Markt (old market), among them a very grand building with large romanesque windows. So at the beginning of the 13th century there were already definite settlements outside of the wall. It was necessary to consider constructing a new far-reaching city wall, which enclosed all built-upon areas and also included a part of the damp Vorgerland, which was unsuitable for building, the later Ölderich.
It is very difficult to assign a definite date for the construction of this wall, for which a few decades were certainly necessary. Various considerations lead to a dating of the end of the 13th century. It would be conceivable to think that the Count of Kleve favored the construction with the intention of securing a fast outpost on the border of the Bergisch Land. This time also fits in with the use of the still relatively new buildings, bricks, which were brought in especially for the foundations and the gallery arcades.
How the walls looked is best shown by the Corputius map of 1566. We can recognize 21 towers and half-towers and four gates (Stapeltor, Kuhtor, Marientor and Schwanentor). Of these walls, which (as far as we know) were the third fortification in Duisburg, about 30% still remains. The full Schlaferturm, the remains of the Schwanentor and the restored stretch on the Obermauerstraße are the best known of these remains.
The area encompassed by this wall was sufficient until the 19th century.
As a fortification, the walls were not tested in earnest. They were able to give protection during a surprise attack, that of the Archbishop of Köln in 1445. However with a width of less than one meter, they would have been hard put to withstand middle age siege machines. With the introduction of cannon, the worth of even more massive walls became dubious. Now ramparts were necessary. A town plan of the 17th century shows Duisburg defended in such a manner. Admiteddly it only existed in the imagination of the artist. This layoout was never carried out. Duisburg relied on diplomatic skills and bribery whenever siege threatened It has to be said that in this manner, it has come through comparatively well through the war-torn centuries.
At the turn of the 19th century, they finally got tired of the walls and its gates and the maintenance costs associated with them. In 1815, the Schwanentor was the first gate to be demolished, in 1833 the Kuhtor was the last to go.