Question: The Melanchthon Circle was a 16th-century Lutheran intellectual network centred on the University of Wittenberg in Germany, and its leading theologian Philip Melanchthon, patronage came from which 37th Grand Master of the Teutonic Knights, who after converting to Lutheranism, became the first ruler of the Duchy of Prussia, the secularized state that emerged from the former Monastic State of the Teutonic Knights?

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List of monarchs of Prussia: The monarchs of Prussia were members of the House of Hohenzollern who were the hereditary rulers of the former German state of Prussia from its founding in 1525 as the Duchy of Prussia.  The Duchy had evolved out of the Teutonic Order, a Roman Catholic crusader state and theocracy located along the eastern coast of the Baltic Sea.  The Teutonic Knights were under the leadership of a Grand Master, the last of whom, Albert, converted to Protestantism and secularized the lands, which then became the Duchy of Prussia.  The Duchy was initially a vassal of the Kingdom of Poland, as a result of the terms of the Prussian Homage whereby Albert was granted the Duchy as part of the terms of peace following the Prussian War.  When the main line of Prussian Hohenzollerns died out in 1618, the Duchy passed to a different branch of the family, who also reigned as Electors of Brandenburg in the Holy Roman Empire.  While still nominally two different territories, Prussia under the suzerainty of Poland and Brandenburg under the suzerainty of the Holy Roman Empire, the two states are known together historiographically as Brandenburg-Prussia.  Following the Second Northern War, a series of treaties freed the Duchy of Prussia from any vassalage to any other state, making it a fully sovereign Duchy in its own right.  This complex situation (where the Hohenzollern ruler of the independent Duchy of Prussia was also a subject of the Holy Roman Emperor as Elector of Brandenburg) laid the eventual groundwork for the establishment of the Kingdom of Prussia in 1701.  For diplomatic reasons, the rulers of the state were known as the King in Prussia from 1701 to 1772; largely because they still owed fealty to the Emperor as Electors of Brandenburg, the "King in Prussia" title (as opposed to "King of Prussia") avoided offending the Emperor.  As the Prussian state grew through several wars and diplomatic moves throughout the 18th century, it became apparent that Prussia had become a Great Power that did not need to submit meekly to the Holy Roman Empire.  By 1772, the pretense was dropped, and the style "King of Prussia" was adopted.  Thus it remained until 1871, when in the aftermath of the Franco-Prussian War, the King of Prussia Wilhelm I was crowned German Emperor.  From that point forward, though the Kingdom of Prussia retained its status as a constituent state of the German Empire, all remaining Kings of Prussia also served as German Emperor, and that title took precedence.

Peace of Thorn (1411): The (First) Peace of Thorn was a peace treaty formally ending the Polish–Lithuanian–Teutonic War between allied Kingdom of Poland and Grand Duchy of Lithuania on one side, and the Teutonic Knights on the other.  It was signed on 1 February 1411 in Thorn (Toruń), one of the southernmost cities of the Monastic State of the Teutonic Knights.  In historiography, the treaty is often portrayed as a diplomatic failure of Poland–Lithuania as they failed to capitalize on the decisive defeat of the Knights in the Battle of Grunwald in June 1410.  The Knights returned Dobrzyń Land which they captured from Poland during the war and made only temporary territorial concessions in Samogitia, which returned to Lithuania only for the lifetimes of Polish King Władysław Jagiełło and Lithuanian Grand Duke Vytautas.  The Peace of Thorn was not stable.  It took two other brief wars, the Hunger War in 1414 and Gollub War in 1422, to sign the Treaty of Melno that solved the territorial disputes.  However, large war reparations were a significant financial burden on the Knights, causing internal unrest and economic decline.  The Teutonic Knights never recovered their former might.

Polish–Teutonic War (1519–21): The Polish–Teutonic War of 1519–1521 (German: "Reiterkrieg" , "horsemen's war", Polish: "Wojna pruska" , "Prussian War") was fought between the Kingdom of Poland and the Teutonic Knights, ending with an armistice in April 1521.  Four years later, under the Treaty of Kraków, part of the Catholic Monastic state of the Teutonic Knights became secularized as the Duchy of Prussia.  The reigning Grand Master Albert of Hohenzollern-Brandenburg-Ansbach became the first Duke of Prussia by paying the Prussian Homage as vassal to his uncle, Polish king Sigismund I the Old.

Albert, Duke of Prussia: Albert of Prussia (German: Albrecht von Preussen, 17 May 149020 March 1568) was the 37th Grand Master of the Teutonic Knights, who after converting to Lutheranism, became the first ruler of the Duchy of Prussia, the secularized state that emerged from the former Monastic State of the Teutonic Knights.  Albert was the first European ruler to establish Lutheranism, and thus Protestantism, as the official state religion of his lands.  He proved instrumental in the political spread of Protestantism in its early stage, ruling the Prussian lands for nearly six decades (1510–1568).

Battle of Grunwald: The Battle of Grunwald, First Battle of Tannenberg or Battle of Žalgiris, was fought on 15 July 1410 during the Polish–Lithuanian–Teutonic War.  The alliance of the Kingdom of Poland and the Grand Duchy of Lithuania, led respectively by King Władysław II Jagiełło (Jogaila) and Grand Duke Vytautas, decisively defeated the German–Prussian Teutonic Knights, led by Grand Master Ulrich von Jungingen.  Most of the Teutonic Knights' leadership were killed or taken prisoner.  Although defeated, the Teutonic Knights withstood the siege of their fortress in Marienburg (Malbork) and suffered minimal territorial losses at the Peace of Thorn (1411) (Toruń), with other territorial disputes continuing until the Peace of Melno in 1422.  The knights, however, would never recover their former power, and the financial burden of war reparations caused internal conflicts and an economic downturn in the lands under their control.  The battle shifted the balance of power in Central and Eastern Europe and marked the rise of the Polish–Lithuanian union as the dominant political and military force in the region.

Treaty of Salynas: Treaty of Salynas (German: "Frieden von Sallinwerder" , Lithuanian: "Salyno sutartis" ) was a peace treaty signed on 12 October 1398 by the Grand Duke of Lithuania Vytautas the Great and the Grand Master of the Teutonic Knights Konrad von Jungingen.  It was signed on an islet of the Neman River, probably between Kulautuva and the mouth of the Nevėžis River.  It was the third time, after the Treaty of Königsberg (1384) and Treaty of Lyck (1390), that Vytautas promised Samogitia to the Knights.  The territory was important to the Knights as it physically separated the Teutonic Knights in Prussia from its branch in Livonia.  It was the first time that the Knights and Vytautas attempted to enforce the cession of Samogitia.  However, it did not solve the territorial disputes over Samogitia and they dragged on until the Treaty of Melno in 1422.

Flag of Prussia: The state of Prussia had its origins in the separate lands of the Margraviate of Brandenburg and of the Duchy of Prussia.  The Margraviate of Brandenburg developed from the medieval Northern March of the Holy Roman Empire, passing to the House of Hohenzollern in 1415.  The Duchy of Prussia originated in 1525 when Albert of Brandenburg-Ansbach, a member of a cadet branch of the Hohenzollerns, secularized the eastern lands of the Teutonic Knights as a Polish fief.  Prince-elector John Sigismund, Elector of Brandenburg, inherited the Duchy of Prussia in 1618, thus uniting Brandenburg and Prussia under one ruler in a personal union; the Elector's state became known as Brandenburg-Prussia.  The Kingdom of Prussia formed when Elector Frederick III assumed the title of Frederick I, King in Prussia, on 18 January 1701.

Battle of Bornholm (1456): The Battle of Bornholm was a naval battle which took place near the Danish island of Bornholm, between privateers from the city of Gdańsk (Danzig) and a transport convoy of Danish and Livonian ships which were attempting to bring supplies and reinforcements to the Teutonic Knights in Prussia, during the Thirteen Years' War (1454–66) between the Kingdom of Poland and the Prussian Confederation on one hand, and the Monastic State of the Teutonic Knights on the other.  The battle took place on the night of 14 August 1457.

Melanchthon Circle: The Melanchthon Circle was a 16th-century Lutheran intellectual network centred on the University of Wittenberg in Germany, and its leading theologian Philip Melanchthon.  It was identified as significant for its interests in natural philosophy by Lynn Thorndike, in a chapter "The Circle of Melanchthon" in his multi-volume "History of Magic and Experimental Science".  Among this circle were found many of the most important early proponents of the heliocentric model of Copernicus.  They included Caspar Peucer who became Melanchthon's son-in-law, Erasmus Reinhold, and Georg Joachim Rheticus.  Patronage came from Albert, Duke of Prussia.

Prussian Crusade: The Prussian Crusade was a series of 13th-century campaigns of Roman Catholic crusaders, primarily led by the Teutonic Knights, to Christianize the pagan Old Prussians.  Invited after earlier unsuccessful expeditions against the Prussians by Polish princes, the Teutonic Knights began campaigning against the Balts in 1230.  By the end of the century, having quelled several Prussian Uprisings, the Knights had established control over Prussia and administered the Prussians through their monastic state.

Supporting paragraphs: Melanchthon Circle Albert, Duke of Prussia
Answer: Albert of Prussia