Prizren Fortress , also known as Kaljaja (Albanian: Каlаја, Serbian Cyrillic: Каљаја) and Dušan's Fortress (Душанов град/Dušanov grad), is a medieval fortress in Prizren, Kosovo,[a] which once served as the capital of the Serbian Empire. It was built on a hill above Prizrenska Bistrica, around which the modern city developed. The first fort, erected on this location by the Byzantines, was further expanded by Emperor Stefan Dušan (r. 1331–55). The fort then came under the control of the Ottomans for four centuries. It was declared a Monument of Culture of Exceptional Importance in 1948.