Konrad I of Masovia (ca. 1187/88 – 31 August 1247), from the Polish Piast dynasty, was the sixth Duke of Masovia and Kuyavia from 1194 until his death as well as High Duke of Poland from 1229 to 1232 and again from 1241 to 1243. Life Konrad was the youngest son of High Duke Casimir II the Just of Poland and Helen of Znojmo, daughter of the Přemyslid duke Conrad II of Znojmo (ruler of the Znojmo Appanage in southern Moravia, part of Duchy of Bohemia). His maternal grandmother was Maria of Serbia, apparently a daughter of the pre-Nemanjić župan Uroš I of Rascia. After his father's death in 1194, Konrad was brought up by his mother, who acted as regent of Masovia. In 1199, he received Masovia and in 1205 the adjacent lands of Kuyavia as well. In 1205, he and his brother, Duke Leszek I the White of Sandomierz, had their greatest military victory at Battle of Zawichost against Prince Roman the Great of Galicia–Volhynia. The Ruthenian army was crushed and Roman was killed in battle. The Rurik princess Agafia of Rus became his wife. Attempted conquests of Prussia In an effort to enlarge his dominions, Konrad unsuccessfully attempted to conquer the adjacent pagan lands of Chełmno in Prussia during a 1209 crusade with the consent of Pope Innocent III. In 1215, the monk Christian of Oliva was appointed a missionary bishop among the Old Prussians, his residence at Chełmno however was devastated by Prussian forces the next year. Several further campaigns in 1219, 1222 failed, instead Konrad picked a long-term border quarrel with the Prussian tribes. The duke's ongoing attempts on Prussia were answered by incursions across the borders of his Masovian lands, while Prussians were in the process of gaining back control over the disputed Chełmno Land and even threatened Konrad's residence at Płock Castle. Subjected to constant Prussian raids and counter-raids, Konrad now wanted to stabilize the north of his Duchy of Masovia in this fight over the border area of Chełmno. Teutonic Order Thus in 1226, Konrad, having difficulty with constant raids over his territory, invited the religious military order of the Teutonic Knights to fight the Prussians, as they already had supported the Kingdom of Hungary against the Cuman people in the Transylavanian Burzenland from 1211 to 1225. When they notified Hungary that the Order was, firstly, responsible to the pope, the Knights