Between 1561 and 1729, Plön was the capital of the Duchy of Schleswig-Holstein-Sonderburg-Plön. The Duchy of Schleswig-Holstein-Plön emerged in 1622 as a result of succession in the Danish royal house. From 1633 to 1636 a Renaissance castle was built on the site of the old castle by Duke Joachim Ernest, and Plön became the capital of the small but independent princedom. As a residence town Plön experienced a considerable increase in status. For example, in 1685 Duke John Adolphus (""Hans Adolf"") founded the new town ("Neustadt") northwest of the town in order to settle craftsmen here and thus increase the economic might of the duchy. Under Charles Frederick the castle district was expanded with several baroque buildings and a pleasure garden. At that time the town had about 1,000 inhabitants and reached as far as the bridge over the Schwentine in the east and as far as the end of today's pedestrian zone in the west. Both entrances were protected by gates.