during the campaign; in exchange, the Order returned Zawkrze to Siemowit IV, despite the fact that under the Peace of Thorn (1411) they aren't obliged to do it. Despite his official subordination to Poland, Siemowit IV tried to pursue an independent foreign policy. This was expressed in his frequent contacts with the Hungarian King Sigismund, who, wishing to drag a Polish vassal to his side gave the Masovian Duke the rich prebends from the Bishopric of Veszprém and other possessions across Hungary. Siemowit IV's relations with Poland, although some temporary frictions caused by his too independent policy (he even minted his own coins) remained friendly, despite the fact that he didn't fulfill his duties as a vassal, and only sent troops to Poland occasionally when he was required to do. Another gesture of friendship with King Władysław II was noted when he used Siemowit IV's daughters into political marriages and the support given to his son Alexander in his Church career. In domestic politics, Siemowit IV continued the economic restructuring which begun under the rule of his father. For this purpose, in addition to the existing statutes he implemented the Kulm law in several of his cities and promoted the colonization of the Masovian nobility to Belz. Ill health and death After 1420 Siemowit IV, due to his progressive blindness, gradually gave participation in the government to his adult sons. In 1425, the dispute about the election of his Chancellor Stanisław z Pawłowic as Bishop of Płock forced his sons Siemowit V and Casimir II into a humiliating surrender. Siemowit IV died on 21 January 1426 at Gostynin and was buried in the Ducal crypt at Płock Cathedral. Marriage and Issue In 1387, Siemowit IV married Alexandra (d. 20 April 1434), a Lithuanian princess, daughter of Algirdas, Grand Duke of Lithuania, and his second wife, Uliana of Tver. They had thirteen children: Siemowit V (1389 - 17 February 1442). Hedwig (ca. 1392 - aft. 19 February 1439), married after 3 January 1410 to Janos Garai, Ban of Uzora and Obergespan of Temes and Pozsega. Cymburgis (ca. 1394 - 28 September 1429), married on 25 January 1412 to Ernest I, Duke of Austria. Euphemia (1395/97 - bef. 17 September 1447), married on 20 November 1412 to Bolesław I, Duke of Cieszyn. Amelia (1397/98 - aft. 17 May 1434), married on 16 May 1413 to William II, Margrave of Meissen. Alexander (1400