XI. (1501-1573), son of Bogislaus X., duke of Pomerania, became duke on his father's death in 1523. He ruled for a time in common with his elder brother George; and after George's death in 1531 he shared the duchy with his nephew Philip I., retaining for himself the duchy of Pomerania-Stettin. The earlier years of his rule were troubled by a quarrel with the margrave of Brandenburg, who wished to annex Pomerania. In 1529, however, a treaty was made which freed Pomerania from the supremacy of Brandenburg on condition that if the ducal family became extinct the duchy should revert to Brandenburg. Barnim adopted the doctrines of Martin Luther, and joined the league of Schmalkalden, but took no part in the subsequent war. But as this attitude left him without supporters he was obliged to submit to the emperor Charles V., to pay a heavy fine, and to accept the Interim, issued from Augsburg in May 15 4 8. In 1569 Barnim handed over his duchy to his grand-nephew, John Frederick, and died at Stettin on the 2nd of June 1573.