Sigmaringen Castle on the Danube River. The seat of the Swabian Princes Hohenzollern-Sigmaringen. First mentioned in 1077 during an unsuccessful siege by the Duke of Swabia against Henry IV of Germany. The original owner was a Ludwig von Sigmaringen. In 1540, the castle was taken over by the Hohenzollerns, founding the Hohenzollern-Sigmaringen line.