According to the Medieval Chronicle of Greater Poland (Kronika Wielkopolska) Koszalin was one of the Pomeranian cities captured and subjugated by Duke Bolesław III Wrymouth of Poland in 1107 (other towns included Kołobrzeg, Kamień and Wolin).
Afterwards, in the 12th century the area became part of the Griffin-ruled Duchy of Pomerania, a vassal state of Poland, which separated from Poland after the fragmentation of Poland into smaller duchies, and became a vassal of Denmark in 1185 and a part of the multi-ethnic Holy Roman Empire from 1227 to 1806.

In 1214, Bogislaw II, Duke of Pomerania, made a donation of a village known as Koszalice/Cossalitz by Chełmska Hill in Kołobrzeg Land to the Norbertine monastery in Białoboki near Trzebiatów.
New, mostly German, settlers from outside of Pomerania were invited to settle the territory.
In 1248, the eastern part of Kołobrzeg Land, including the village, was transferred by Duke Barnim I to the Roman Catholic Diocese of Kammin.

On 23 May 1266, Kammin bishop Hermann von Gleichen granted a charter to the village, granting it Lübeck law, local government, autonomy and multiple privileges to attract German settlers from the west.
When in 1276 the bishops became the sovereign in neighboring Kołobrzeg, they moved their residence there, while the administration of the diocese was done from Koszalin.
In 1278 a Cistercian monastery was established, which took care of the local parish church and St. Mary chapel on Chełmska Hill.

The city obtained direct access to the Baltic Sea when it gained the village of Jamno (1331), parts of Lake Jamno, a spit between the lake and the sea and the castle of Unieście in 1353.
Thence, it participated in the Baltic Sea trade as a member of the Hanseatic League (from 1386), which led to several conflicts with the competing seaports of at Kołobrzeg and Darłowo.
From 1356 until 1417/1422, the city was part of the Duchy of Pomerania-Wolgast.
In 1446 Koszalin fought a victorious battle against the nearby rival city of Kołobrzeg.
In 1475 a conflict between the city of Koszalin and the Pomeranian duke Bogislaw X broke out, resulting in the kidnapping and temporary imprisonment of the duke in Koszalin.
According to the Medieval Chronicle of Greater Poland (Kronika Wielkopolska) Koszalin was one of the Pomeranian cities captured and subjugated by Duke Bolesław III Wrymouth of Poland in 1107 (other towns included Kołobrzeg, Kamień and Wolin). Afterwards, in the 12th century the area became part of the Griffin-ruled Duchy of Pomerania, a vassal state of Poland, which separated from Poland after the fragmentation of Poland into smaller duchies, and became a vassal of Denmark in 1185 and a part of the multi-ethnic Holy Roman Empire from 1227 to 1806.
In 1214, Bogislaw II, Duke of Pomerania, made a donation of a village known as Koszalice/Cossalitz by Chełmska Hill in Kołobrzeg Land to the Norbertine monastery in Białoboki near Trzebiatów. New, mostly German, settlers from outside of Pomerania were invited to settle the territory. In 1248, the eastern part of Kołobrzeg Land, including the village, was transferred by Duke Barnim I to the Roman Catholic Diocese of Kammin.
On 23 May 1266, Kammin bishop Hermann von Gleichen granted a charter to the village, granting it Lübeck law, local government, autonomy and multiple privileges to attract German settlers from the west. When in 1276 the bishops became the sovereign in neighboring Kołobrzeg, they moved their residence there, while the administration of the diocese was done from Koszalin. In 1278 a Cistercian monastery was established, which took care of the local parish church and St. Mary chapel on Chełmska Hill.
The city obtained direct access to the Baltic Sea when it gained the village of Jamno (1331), parts of Lake Jamno, a spit between the lake and the sea and the castle of Unieście in 1353. Thence, it participated in the Baltic Sea trade as a member of the Hanseatic League (from 1386), which led to several conflicts with the competing seaports of at Kołobrzeg and Darłowo. From 1356 until 1417/1422, the city was part of the Duchy of Pomerania-Wolgast. In 1446 Koszalin fought a victorious battle against the nearby rival city of Kołobrzeg. In 1475 a conflict between the city of Koszalin and the Pomeranian duke Bogislaw X broke out, resulting in the kidnapping and temporary imprisonment of the duke in Koszalin.
Koszalin