The town was surrounded by defensive walls at the end of the 13th century. In the next century fortifications were developed. In the eighteenth and nineteenth centuries, due to the expansion of the town and the loss of military significance, the walls were almost completely demolished.
The fortifications were built of large granite pebbles, only their superstructure was finished with burnt bricks. It surrounded the town with an irregular quadrangle surrounded by an irrigated and sometimes dry moat. From the north, south and east, the perimeter was reinforced with a number of regularly arranged four-sided half towers. They were not only from the west, where the town bordered the outer wards of the Teutonic castle and the church of St. Nicholas, and from the north-west where the upper castle was located. The vulnerable southern corner was defended by a closed, cylindrical tower, while in close proximity to the north-eastern curtain of the walls the town was protected by the Kowalewskie Lake. Two main gates led to the town: Toruńska Gate from the south and Brodnicka Gate from the north. In addition, a wicket led to the castle, and a Water Gate was located in the north-eastern part of circuit.
To this day, a corner, cylindrical tower and a fragment of the wall at Fosa Jagiellońska street have survived. The latter, however, is already a fragment of the southernmost castle ward.