the komturs of Ostróda and Pokarmin invaded Janusz's domains. In retaliation, Janusz I's son Bolesław destroyed Działdowo and 14 surrounding villages. Between 1409-1411 Janusz I continued his support to Władysław II Jagiełło in the great war against the Teutonic Order and fielded a banner of cavalry to aid the Polish King. In the village of Czerwińsk nad Wisłą, Janusz I designated the place of concentration of the united Polish-Lithuanian army. From there him, at the head his army organized their squadrons of knights and went to Grunwald, where on 15 July 1410 took place the battle. Janusz I then participated in the rest of the campaign. Władysław II, as way to recompensate his fidelity, give to him the Teutonic castles of Nidzica, Ostróda and Olsztyn. However, this acquisitions weren't permanent, because seven months later (1 February 1411) after the sign of the Peace of Thorn, he was forced to return the castles to the Teutonic Order. When in 1414 another war broke out with the Teutonic Knights (the called Hunger War), Janusz I again decided to support the King. This time, however, probably because of his advanced age, he didn't participated directly in the campaign but send his son Bolesław. Internal Policy and Reforms In domestic politics, Janusz I took a thorough reform of the economic policies of the principality given the German Kulm law to 24 cities including Czersk (1383), Ciechanów (1400), Różan (1403), Warsaw New Town (1408), Drohiczyn (1408), Łomża (1418), Grójec (1419), Maków Mazowiecki and Mińsk Mazowiecki (1421), Kolno and Tykocin (1425), Przasnysz and Ostrołęka (1427) and Kamieńczyk (1428). An extremely important step took place in 1406, when he moved his capital from Czersk to newly developing strategic town of Warsaw and actively worked to develop his towns, fortified his castles and strongholds. A clear sign of this develop was the creation of a Collegiate at St. John Church and the build of a castle (who was later known as the oldest part of the future Royal Palace). Among the most notorious castles fortified during this time are the former capital Czersk, Liw and Ciechanów. Marriage and Issue Around 23 November 1371/73, Janusz I married the Lithuanian princess Danutė (c. 1358 - c. 24 November 1424) -who in baptism took the name Ana-, a daughter of Kęstutis and sister of Vytautas, both Dukes of Trakai and Grand Dukes of Lithuania; in consequence, she was a first-cousin of