The zenith of Serbian power was reached in 1346, with the formation of the Serbian Empire(1346-1371). During the 13th and 14th centuries, Kosovo became a political, cultural and religious centre of the Serbian Kingdom. In the late 13th century, the seat of the Serbian Archbishopric was moved to Peja, and rulers centred themselves between Prizren and Skopje, during which time thousands of Christian monasteries and feudal-style forts and castles were erected. Stefan Dušan used Prizren Fortress as one of his temporary courts for a time. When the Serbian Empire fragmented into a conglomeration of principalities in 1371, Kosovo became the hereditary land of the House of Branković. In the late 14th and the 15th centuries parts of Kosovo, the easternmost area of which was located near Pristina, were part of the Principality of Dukagjini, which was later incorporated into an anti-Ottoman federation of all Albanian principalities, the League of Lezhë.