Since the beginning of the 13th century, Zalewo was an important stronghold against Prussians and Lithuanians. Its strategic importance was appreciated by the Teutonic Knights, raising the watchtower here in the 13th century. After the conquest of Pogesania and Warmia, the Zalewo lost its importance, however, the settlement developed, inhabited mostly by settlers from Saxony. The fortified walls in Zalew were built by the burghers with the help of the Teutonic Order from the beginning of the 14th to the 15th century. The demolition process lasted from the end of the 18th century to the middle of the 19th century.
City walls were built of field stones and bricks. Its thickness was not uniform everywhere. On the north side, where the steep and high embankment formed a natural strengthening, the wall was wide at about 63 cm. On the other three sides, where the slope is mild, the wall was much wider and had a thickness of about 120 cm. There were two gates within it: Kupińska, also called Morąska and the Przezmarcka, and nineteen towers extending beyond the wall. On the outside of the wall was a deep moat filled with water.
Only small fragments of the defensive wall with remodeled tower next to the parish church survived.
Sypek A., Sypek.R., Zamki i obiekty warowne od Malborka do Torunia, Warszawa 2004.
Website zamkidwory.forumoteka.pl, Zalewo.