Kętrzyn was surrounded by town walls in the years 1350-1378, after invasions and destruction incurred during the Lithuanian invasions from 1344 and 1347. Initially, there were timber and earth fortifications, which were gradually transformed into masonry. In the privilege from 1357, there are already two urban gates mentioned: “the gate from the side of Sątoczno” (later called the High Gate) and “the gate from the side of the mill”. The town was probably planned in advance, as one compact defense system, integrated with the castle and the fortified church of St. George.
Kętrzyn has long cared for the good condition of fortifications, helping with the collection of fees from goods imported into the town. It was also important to protect the city against foreigners, as various epidemics appeared in Prussia. In 1646 and 1648, the walls at the Mill Gate and the brick bridge in front of the High Gate were repaired. In 1653, roof covers on porches running at the top of the walls were replaced and the drawbridge suspended over the moat in front of the Mill Gate was repaired. In 1698, the existing wall breaks were patched with a palisade, and in 1700 the tower and a large part of the wall near the High Gate were rebuilt, which collapsed in the previous year. Thanks to this concern, it was possible to effectively protect the town against the plague epidemic that wreaked havoc in the years 1708-1711. Only three people died in Kętrzyn.
The second half of the 18th century brought destruction to the town’s fortifications. The great town fire of 1761 caused the demolition of defensive walls, which became a source of cheap building material for the reconstruction of the destroyed city. Both town gates were demolished in the first quarter of the 19th century.
The defensive wall was erected on the plan of an irregular quadrangle. In the south-west corner, the defensive function was served by the basilica of St. George, and in the south-east by the castle. The walls were built of brick on a stone plinth with a width of over 1 meter. Their height reached 10 meters. Later, they were crowned with a roof above the sidewalk of defenders, perhaps earlier they had only battlements. Walls were strengthened by 13 towers, their layout is not exactly known today, certainly were placed in the north – east and north – west corner. Two gates led to the town: High and Mill on the north-south line, and additionally a water wicket gate at the church. This way led to the mill pond, which was, among other things, a source of water to extinguish frequent fires. The Mill Gate was placed near the castle, in the southern belt of the defensive walls, protected both by the backwaters and the proximity of the castle itself. Both gates were placed in the towers, the entrance to the High Gate was additionally flanked by two towers, protruded from the face of the walls. On the external side, there was a fairly wide zwinger, in front of the second, lower wall with an additional foregate. Each gate was preceded by a moat and a drawbridge. The High Gate defensive system was probably dictated by the weak defensive features of the area, which from the north was relatively flat.
To this day, the best preserved part of the fortifications is at the back of the church of St. George, in the north-west part and the tower in the north-eastern corner of the old town.
Webpage jerzysikorski.pl, Historia miasta Kętrzyn.