The city fortifications of the former Electorate of Cologne customs fortress of Zons, planned by Archbishop Friedrich von Saarwerden between 1373 and 1408, are almost completely preserved with the surrounding city wall, the corner towers and guardhouses as well as the ditches, ramparts and the forecourt. The city wall with the watchtowers was built as a regular rectangular structure made of columnar basalt, trachyte, tuff and brick.
The four corner towers include the six-storey, almost 26m high Rhine Tower, completed in 1388, with the remains of the gate system of the former Rhine Gate, which was also used as a customs tower for collecting the Rhine toll. The round Krötschen Tower and the Mill Tower form the western corner towers of the city fortifications, the former Field Gate in between, the second main gate of the city fortifications, was demolished between 1833 and 1842. The mill tower shows the still completely preserved mill technology with the grinding mechanism of the former mill. In front of the south wall is the moat wall with the south-east corner round tower, the "icebreaker".
The state castle, built by Archbishop Friedrich von Saarwerden from 1373 onwards when the entire city complex was built, served to secure customs revenues for over four centuries. Columnar basalt, trachyte, tuff and brick were used for the almost square complex with the city wall in the south and east and the moat in front in the north and west. The most striking and also oldest building in the stronghold is the mighty gate tower, which was the only access to the inner courtyard in the Middle Ages. The double gate system of the south gate was the only gate leading directly into the outer bailey, which was bordered by high walls on the sides facing the city. The Juddeturm, equipped with loopholes and machicolations, in the basement of which is the windowless castle dungeon, is the northwestern fortification tower of the outer bailey.
Source: swd-dormagen.de/fileadmin/civserv/pdf-felder/fachbereich_6/Denkmalschutz-Rundgang/Internetversion_opti.pdf