was taken by Polish forces on 18 March 1520. Polish forces under
Grand Crown Hetman Mikołaj Firlej gathered near
Koło and in January struck towards
Pomesania towards
Königsberg, laying
siege to Marienwerder (now
Kwidzyn) and Preußisch Holland (now
Pasłęk). The siege was slow, however, since the Polish forces lacked
artillery power. The Polish fleet began a
blockade of Teutonic ports. The Knights, in the meantime, took the Warmian city of Braunsberg (now
Braniewo). The Polish army received artillery reinforcements in April and took Marienwerder and Preußisch Holland that month, but failed to retake Braunsberg. The war grew, with Polish forces from the
Duchy of Masovia and
Gdańsk striking the nearby Teutonic fortifications. Teutonic forces were on defense, waiting for reinforcements from Germany, which arrived in the summer of 1520. In July, the Teutonic army started an offensive, attacking Masovia, Warmia, and
Łomża territories, laying siege to
Lidzbark Warmiński. In August, another group of German reinforcements attacked
Greater Poland, taking
Międzyrzecz. The Germans took
Wałcz,
Chojnice,
Starogard Gdański, and
Tczew and started a siege of Gdańsk, but they retreated when faced with Polish reinforcements and plagued by financial troubles (German reinforcements, mostly mercenaries, refused to fight until paid). Polish forces retook Tczew, Starogard, and Chojnice. The Teutonic Knights retreated towards
Oliwa and
Puck, pursued by Polish forces. The Polish side was then struck with financial troubles, and the "
pospolite ruszenie" forces were also tired. The Teutonic Knights seized their chance and launched a counteroffensive, taking
Nowe Miasto Lubawskie and approaching
Płock and
Olsztyn. Olsztyn was
successfully defended by the Poles under the command of
Nicolaus Copernicus. At that point, the
Ottoman Empire invaded Hungary, and the new Holy Roman Emperor,
Charles V, demanded that the Teutonic Knights and Poles stop their hostilities and aid the defense of Europe against the infidels. Both sides, tired with the war, agreed to an
armistice on 5 April 1521 in the
Compromise of Thorn. ==Aftermath==