After 1307, when Slupsk came under control of Brandenburg margraves, they issued an important document on 9th September 1310. It was a relocation, confirmation of town rights given to the town in 1265 on the basis of the Magdeburg law. One of privileges guaranteed by this document was releasing the town from any tributes or payments for a period of 10 years, but only after surrounding the town with a wooden palisade. We can nowadays suppose that in some following years this condition was met. In Wartislaw IV's document from 1325, when the duke confirmed giving landed estates in Slupsk to Dominicans, we can find information that makes us think the town had already been surrounded with the palisade.

They began constructing regular defence walls after 1325. Due to the fact that in wooden constructions the weakest and most exposed place to attack were gates, in the beginning bottom parts of three gates in Slupsk were built – the Holstein Gate from the north (route to Ustka), also called the Carpenter's gate, Miller's Gate from the east (route from Gdansk to Szczecin), New Gate from the west (on axis of the route). In the second stage of constructing fortifications in Slupsk, the height of these gates was raised by another floors and walls from the south, west and north were put up. From duke Boguslav V's document, it is clear that in 1374 most of town walls were already in place.

Another fortifications within the town's defence system were built in 15th century. They included the wall along the Slupia River together with the Witches Tower that has remained up to this day. In the half of 15th century, gatehouses of the New Holstein Gates were built. Near the Holstein Gate, the Porridgy and Powder wall towers were also situated. We have no information on their construction details but their names can be found in documents coming from that period. Apart from gates already mentioned, there were also another ones which were actually town wicket gates for pedestrians. An example of such a wicket gate may be the Smith's Gate from 15th century situated in the east of the town (neighbourhood of the Armia Krajowa Street), as well as Monk's Gate situated near the Dominican monastery and Owlish Gate situated at the end of today's Lukasiewicza Street towards the west.

In the following century, in 1507, duke Boguslav X put up a castle which completed the fortifications from the south-east . In the town's fortification system, a basic defence element were wall towers and bays (curved walls sticking out from the rest of the building, on rectangular plan, tightly joined to the wall). In medieval Slupsk, a total circumference of walls with towers was about 2400 metres. Walls were built from bricks put onto the stone foundation. At the top, they had the straight finial without battlements (a low wall around the top of castle with spaces in it that people inside could shoot through). From the first stage of the development, fragments of north and west walls have remained up to this day. The highest parts have 6 metres in height and up to 1 metre in width. Next to walls coming from this period, we can discover two types of wall towers, bays in fact, 6,5 and 3 metres in width. They stuck out of the front of a wall.

In east and south segments, walls from the second stage of the defence building system with a bit different structure – arcs supported on the stone foundation – have been preserved. They have recesses where shooting stations, joined to each other by platform for defenders, were located. Newer walls of the east side of the town had a different type of towers than bays mentioned above. Up to this day, two towers belonging to this part of buildings have remained. The Witches Tower based on a semicircular wall sticking “outside” and rectangular part open towards the town. The tower had its own dark history too, since in 17th century it was used as prison and place of tortures for women suspected of practising witchcraft. The second tower called Prison having few fragments slightly above the foundation remained up to nowadays is situated near St. Nicolaus' church (today, this is where a municipal public library is located). The tower was built on circular plan and the larger part of its circumference is located inside the wall.

In 17th century (the Thirty Year's War), there were made very significant modifications to the town's defence system. With the development of firearms, medieval fortifications began to lose their importance. They started to develop a modern defence system which surrounded the town with another earthworks and bastions. Bastions were pentagonal and their base was open towards the town. In Slupsk, the earthwork run along the town's walls on its west side. Three bastions were located in its corners, and gatehouses of New and Holstein Gates became elements of the system. Another obstacle for enemy forces to attack were pools: the Copper pond near the Holstein gate and the Quebbe municipal pond situated in front of the New Gate. In the second half of 19th century, long segments of walls from the north and west side of the town were removed. In 1834, the Powder Tower was knocked down, then thirty years after that the Holstein Gate situated on route to Ustka suffered the same fate. Areas of earthworks and bastions were levelled and then turned into town's promenades and greens.