of Konrad I of Masovia (duke from 1194 to 1247). Teutonic Order In 1226 Duke Konrad I of Masovia invited the Teutonic Knights to Christianize the pagan Prussians. He supplied the Teutonic Order and allowed the usage of Chełmno Land (Culmerland) as a base for the knights. They had the task of establishing secure borders between Masovia and the Prussians, with the assumption that conquered territories would become part of Masovia. The Order waited until they received official authorisation from the Empire, which Emperor Frederick II granted by issuing the Golden Bull of Rimini (March 1226). The papal Golden Bull of Rieti from Pope Gregory IX in 1234 confirmed the grant, although Konrad of Masovia never recognized the rights of the Order to rule Prussia. Later, the Knights were accused of forging these land grants. By the end of the 13th century the Teutonic Order had conquered and Christianized most of the Prussian region, including Warmia. The Teutonic Order recruited mostly German-speaking settlers to develop the land. The new régime reduced many of the native Prussians to the status of serfs and gradually Germanized them. . Native Prussians were also reported as holders of estates. Over several centuries the colonists, native Prussians and immigrants gradually intermingled. Until the early 13th century, also the southern parts of Warmia were German-speaking. Polish settlers arrived later, particularly after 1410, mainly to the south of Warmia, so that German was replaced by Polish in this area. In 1242 the papal legate William of Modena set up four dioceses, including the Archbishopric of Warmia. From the 13th century new colonists, mainly Germans, settled in the Monastic State of the Teutonic Knights incl. Warmia. The bishopric was exempt and was governed by a prince-bishop, confirmed by Emperor Charles IV. The Bishops of Warmia were usually Germans or Poles, although Enea Silvio Piccolomini, the later Pope Pius II, served as an Italian bishop of the diocese. After the 1410 Battle of Grunwald, Bishop Heinrich Vogelsang of Warmia surrendered to King Władysław II Jagiełło of Poland, and later with Bishop Henry of Sambia gave homage to the Polish king at the Polish camp during the siege of Marienburg Castle (Malbork). After the Polish army moved out of Warmia, the new Grand Master of the Teutonic Knights, Heinrich von Plauen the Elder, accused the bishop of treachery and reconquered the region. Kingdom of Poland In February 1440 the nobility