The building of the stone fortifications was begun by the townsfolks of Ośno, similarly to other urban centers of the region, at the turn of the 13th and 14th centuries. After the expansion of the town to the east in the fourteenth century, the old fortifications were demolished and the construction of new ones was begun, while the construction process was certainly quite long. The existence of strong fortifications in the fifteenth century, may be proved by the fact that the siege of the town, undertaken in 1433, and then in 1477, failed, although it must have caused significant damage to the walls. In the last quarter of the fifteenth century, during the removal of the effects of damages, the walls were raised and reinforced with additional towers. Both gates were also extended, and equipped with foregates, protruding far beyond the ring of the walls.
During the Thirty Years War fortifications were partially destroyed and in this condition they survived until 1754. From this year, their reduction began, which started with filling the moats, leveling earth embankments and dismantling the foregates. The gates in the ring of the walls were demolished in the 1870s, leaving wide passages covered with brick pillars. The most damaged half towers were also demolished, walling the gaps created within the walls. The left walls and towers were gradually renovated and strengthen, by numerous buttresses on the outside. At the turn of the 19th and 20th centuries around the walls were marked avenues, which were planted with two rows of lime trees.
The Ośno defensive walls reached a height of 6 meters and ended with brick battlements accessible from the porches situated on the inside. In walls on the level of porches, there were arrowslits. Around the perimeter of the fortifications there was a underwall street, parallel with the width of the smaller town streets.
Fortifications were reinforced with 3 cylindrical towers, 2 semi-circular towers and 12 rectangular half towers, open from the town side. They were all taller than the walls and covered with conical helmets or roofs. The walls of some towers were also topped with battlements. The interiors of the half towers were divided by wooden ceilings, and the entrances were accessible by a ladder. In the Thief’s Tower, situated in the south-east corner, a prison was located from the Middle Ages.
The entrance to the town led through two gates: Sulęcin Gate and Frankfurt Gate. Both were composed of main gates, long necks, drawbridges over the moats and foregates. The gates on the western side with wide arcades were covered with gable roofs. The main gate on the eastern side was covered with a hip roof. In addition to the gates, there were 6 wicket gates in the form of small entrances, closed with solid doors.
In addition to the ring of walls, the town was protected from the south, east and west by a wide moat, and from the north by a marshy area on both sides of the meandering river Łęcza. There were earth ramparts between the moat and the walls.
Currently, the defensive walls are preserved on all the perimeter, except for two crossings on the axes of the former gates and three punches created after demolition of the towers. To this day, there are 2 circular towers, 3 rectangular towers in full height including roofs, 7 half towers, rectangular towers without cover and 4 wicket gates. The height of the walls varies from 2 to 5 meters. The best preserved elements include the Thief’s Tower in which there was a prison, the so-called Bush’s Tower, which in the eighteenth century served as a reserve prison, and three of the half towers, which today are preserved in full height: Wielka Chyżańska Tower, Pitch Tower and Priest Tower. The remaining towers, mostly heavily walled, are preserved only in the ground floor parts. The original forms have four wicket gates, the oldest of which is at the Thief’s Tower, still dates from the Middle Ages.
Pilch.J, Kowalski S., Leksykon zabytków Pomorza Zachodniego i ziemi lubuskiej, Warszawa 2012.
Website osno.pl, zabytki – mury miejskie.