The first wooden residence for the rulers of Pomerania was first erected here in the 13th century, on a hill along the Odra River. More than 100 years later Barnim III made it a building of stone. The Pomeranian Duke's Castle (Zamek Książąt Pomorskich) was then continuously expanded.
http://www.visitpomerania.eu/cities/szczecin/attractions/pomeranian-dukes-castle/