The medieval fortifications in Zemun have been preserved in the remnants of the so called gothic-type citadel. The square castle with a round tower on each side is preserved in parts of its outer walls and towers to the height of 2 meters.
The castle is positioned SE-NW, NE-SW, and the length of its sides is 32.60, 30.15, 32 and 30.80 meters. The average diameter of the towers is 10 meters. The walls are built in broken stone, covered with brick in lime mortar.The fortress was first mentioned in the sources in the ninth century, and then frequently after the twelfth century.
It is believed that the existing walls are from the fourteenth and fifteenth centuries. In a Prandsteter miniature from 1608 the castle is represented as whole and roofed, while the panoramas of Zemun from the eighteenth century show it in ruins. The castle was devastated by the scattering of the building material, and it is necessary to restore and revive it. The ruins of the castle are the oldest remnants of old Zemun.
In 2016 Cultural Heritage Preservation Institute of Belgrade has done a project for reconstruction and restauration of Zemun Fortress.