Duke William IV of Bavaria (1st Half of the 16th Century) Bavaria, an old dukedom long ruled by the native Wittelsbach dynasty, pioneered the transformation of medieval principalities into territorial states. Duke William IV (r. 1508-1550), shown astride his horse in the woodcut below, took two important steps during his rule: he issued the territorial law [Landesordnung] of 1531 and protected his duchy from the spread of Protestantism. Woodcut by Erhard Schoen (1491-1542), first half of the 16th century.