Siege of Allenstein The Siege of Allenstein or the Siege of Olsztyn took place from January 1521 to February 1521 , during the Polish – Teutonic War ( 1519 – 21 ) . The town of Olsztyn ( " Allenstein " ) was defended by Polish forces against those of the German Monastic Order of the Teutonic Knights . The defense of the town was successfully organized and coordinated by Polish astronomer and scholar Nicolaus Copernicus . The Poles successfully resisted the German knights , who eventually had to lift the siege . By the end of 1521 the Teutonic Knights were forced to ask for an armistice and in 1525 the Grand Master of the Order , Albrecht Hohenzollern paid homage to the Polish king , Sigismund the Old . Background . In the 13th century , during the Northern Crusades , the region of the pagan old Prussians had been conquered by the Monastic Order of the Teutonic Knights . In the 15th century , due to discontent with the Order ' s conduct , the Prussians revolted against them . In the Second Peace of Thorn , Royal Prussia became part of the Kingdom of Poland , although with special local privileges . Royal Prussia included the Prince - Bishopric of Warmia ( Ermeland ) , which was surrounded on three sides by the Monastic state . The Polish astronomer Nicolaus Copernicus , who was also a canon ( clerical administrator ) , had been an administrator at Allenstein ( Olsztyn ) from 1516 to 1519 and was a " mainstay of resistance " to the Teutonic Knights there . In 1519 , he left for Frombork ( German : " Frauenburg " ) . In 1511 , Albrecht Hohenzollern became the Grand Master of the Teutonic Order . Like some of the previous Masters , he tried to avoid having to pay homage to the King of Poland of whom he was a vassal . As a result , in 1519 war broke out between the Teutonic Knights and the Kingdom of Poland , with the region of Warmia as a major scene of conflict . Teutonic order troops invaded Warmia in December 1519 with around 5 , 000 soldiers . In January 1520 , they besieged Frauenburg , and eventually burned the whole town , including the houses of the canons ( clerical administrators of Warmia ) and that of Copernicus . The late arrival of Polish troops saved the town ' s cathedral from destruction . As a result , Copernicus was forced to move to Olsztyn where he was put in charge of organizing the defense of the city against the expected attack . He improved the fortifications and stockpiled food and supplies , in the hope that the city could hold out long enough for reinforcements from the king of Poland to arrive . He sent letters to the Polish king asking for extra soldiers to strengthen the 100 - man garrison . As a further precaution , he also sent letters to Elbląg ( Elbing ) with a request for additional supplies and 20 cannons . The letter to the Polish king was intercepted by the knights . Sigismund , however , learned of the threat through other channels and the garrison of the town was expanded to 200 when a unit of infantry , under the leadership of the Czech commander Henryk Peryk of Janowice arrived . Another 700 cavalry under Rotmistrz Zbigniew Slupecki showed up soon after . Further supplies from Elbing , consisting of lead , salt and 16 more artillery pieces arrived in early February . Siege . The Knights arrived at Allenstein on January 16 , 1521 , with a force of some 400 infantry , 600 heavy cavalry , 400 light cavalry , and artillery . They were met by small skirmish units whose purpose was to delay the Knights ' attack for as long as possible . The Teutonic Knights demanded that the town surrender , hoping that a show of force would suffice . Copernicus , however , refused to accede to the demand . On January 26 the Knights launched their assault on the town , led by Wilhelm von Schaumber , near the " Brama Młyńska " ( Mill Gate ) . The Knights managed to approach the walls across the frozen moat and broke through the gate . They hoped to surprise the town ' s defenders . An alarm was sounded , however , and Polish soldiers rushed to the breach in the gate . According to Jerzy Sikorski ( a Polish historian who played a large part in locating Copernicus ’ grave ) , Copernicus probably came out onto the walls and personally directed the Polish defense of the town . The attack was repulsed , and the Teutonic Knights ’ assault force was forced to withdraw . Aftermath . By the end of February , with the arrival of additional reinforcements from Elbląg , the Teutonic Knights were forced to abandon their siege . By the end of 1521 , due to lack of funds to continue the war , and the threat of a large Polish army approaching , they were forced to negotiate with the Polish King . Copernicus represented the Polish side in the armistice negotiations . This was the last time that the Teutonic Knights invaded Warmia . The war ended in 1525 , and on April 10 of that year Albrecht Hohenzollern , now converted to Lutheranism , paid homage to Polish King Sigismund I as a vassal , in what has become known as " the Prussian Homage . " According to the Treaty of Kraków , in return , Albrecht received the eastern portion of Prussia , which became known as Ducal Prussia , in fief from Poland , as a secular duchy , while the western portion , Royal Prussia , together with Warmia , remained under the Polish crown .