for Sigismund's recovery of Brandenburg and his undisputed election as king of the empire later that year. In gratitude for Frederick's services, King Sigismund made him Oberster Hauptmann and Verwalter der Marken (1411). With an iron hand Frederick fought against the rebellious nobility of the March of Brandenburg (in particular, the Quitzow family) and, in the end, restored security. Frederick also became a member of the Parakeet Society and of the League of Constance. At the Council of Constance (30 April 1415) Sigismund granted Frederick the titles of Margrave and Prince-elector of Brandenburg. On 21 October 1415 the Brandenburg states meeting in a Landtag asked him to rule in Berlin. The king awarded him the formal enfeoffment of the margravate on 18 April 1417. As Frederick did not agree with the forcible action of Sigismund against the Hussites, relations between them cooled. Constant feuding with the nobility of Brandenburg led Frederick to withdraw to his castle at Cadolzburg in 1425 and transfer the regency of the margravate to his son John in 1426 (Frederick, however, remained elector). After 1427 he organized the imperial war against the Hussites and subsequently provided substantial assistance in the mediation of the Compacta of Prague at the Council of Basel (30 November 1433). Upon his death in 1440, Frederick was succeeded as elector by his second-eldest son, Frederick II. Family and children He married Elisabeth of Bavaria-Landshut (1383–13 November 1442, Ansbach), daughter of Duke Frederick of Bavaria-Landshut and Maddalena Visconti. Their children were: Elisabeth (1403–31 October 1449, Liegnitz), married: in Konstanz 1418 Duke Louis II of Brieg and Legnica (1380/5–1436); in 1438 Duke Wenzel I of Teschen (1413/18–1474). John "the Alchemist" (1405–1465), Margrave of Brandenburg-Kulmbach. married in 1416 Princess Barbara of Saxe-Wittenberg (1405–1465) Cecilia (c. 1405–4 January 1449), married: in Berlin 30 May 1423 Duke William III of Brunswick-Lüneburg (1392–1482). Margaret (1410–27 July 1465, Landshut), married: in 1423 to Duke Albert V, Duke of Mecklenburg (1397–1423); in Ingolstadt 20 July 1441 to Louis VIII, Duke of Bavaria (1403–1445); in 1446 to Count Martin of Waldenfels (d. 1471). Magdalene (c. 1412 –27 October 1454, Scharnebeck), married: in Tangermünde 3 July 1429 to Duke Frederick of Brunswick-Lüneburg (1418–1478). Frederick II (1413–1471), Elector of Brandenburg married in 1441 Princess Catherine of Saxony (1421–1476) Albert Achilles, (1414–1486), Elector of Brandenburg, married: in 1446 Princess Margarete of Baden (1431–1457) in 1458 Princess Anna of Saxony (1437–1512) Sofie, born and died