The construction of defensive walls in Kościan took place at the end of the fourteenth century or after the year 1400, in which the location privilege was renewed. Later, the fortifications were probably modernized. The extended form of foregate of Gate of Głogów seems to indicate that. The town maybe received a second wall on some sections. The date of reconstruction of the hillfort to a stone castle is unknown. This was perhaps already before the mid-fourteenth century and at the latest during the construction of the town walls. The castle was the seat of the castle starosty, in the hands of the great families of Wielkopolska. Fortifications probably suffered during the wars with the Swedes in the mid-seventeenth century, when the city and the castle were burned. Greater damages were caused to the defensive walls of Kościan in 1704, when the Swedes were again occupied the city. In the 19th century, brick walls were used to build houses, which greatly accelerated the devastation of fortifications. The castle, neglected somewhat in the middle of the 16th century, was 100 years later completely burned by the Swedes and was no longer rebuilt.
The circumference of the defensive walls was marked by a circle, elongated in the south-east direction, for connection with the castle. The area of the town within the walls was about 10 ha, and the length of the fortification line was 1150 meters. Along the town walls there was an unbuilt strip of land in the Middle Ages, only a Dominican monastery in the fifteenth century took a place in the vicinity of the fortifications. The brick defensive wall was no less than 6-7 meters high. Its other dimensions and the way of crowning are not known, it was not reinforced with towers. In the Middle Ages, the city had two gates: Poznań Gate from the north-east and Głogów Gate in the south-western part of the town. Little is known about their architectural form. They were probably located in typical gatehouses, protruding forward of the walls line. The foregate of Głogów Gate was probably built as a result of its extension in the late Middle Ages or early modern times. At the beginning of the 16th century, a gate in the west of the circuit was pierced, leading to the Bernardine monastery.
The Kościan stronghold was not initially associated with the town, but was very close to it. The merger took place during the construction of the town defense walls, which leaned against the castle on both sides. In this way a conjugated defensive complex consisting of the town walls and the adjacent castle was created. Castle had the shape of a regular quadrilateral, close to a square. The entrance was situated in the gate tower led from the side of the town, from which it was divided not only by the wall, but also probably by ditch with water. The main castle house stood from the south. The northern part was occupied by wooden outbuildings, while the eastern part was occupied by the walls of destroyed or never completed three castle’s houses.
The castle has not survived to modern times. From among the town walls only a short fragment remained in the back of the church of Jesus.
Leksykon zamków w Polsce, L.Kajzer, S.Kołodziejski, J.Salm, Warszawa 2003.
Widawski J., Miejskie mury obronne w państwie polskim do początku XV wieku, Warszawa 1973.