The Battle of Grunwald was fought on 15 July 1410 during the Polish–Lithuanian–Teutonic War. The alliance of the Crown 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 Teutonic Order, led by Grand Master Ulrich von Jungingen. Most of the Teutonic Order's leadership was killed or taken prisoner.
https://en.wikipedia.org/wiki/Battle_of_Grunwald
Jan Alojzy Matejko (24 June 1838 – 1 November 1893) was a Polish painter, a leading 19th-century exponent of history painting, known for depicting nodal events from Polish history. His works include large scale oil paintings such as Stańczyk (1862), Rejtan (1866), Union of Lublin (1869), Astronomer Copernicus, or Conversations with God (1873), or Battle of Grunwald (1878). He was the author of numerous portraits, a gallery of Polish monarchs in book form, and murals in St. Mary's Basilica, Kraków. He is considered by many as the most celebrated Polish painter, and sometimes as the "national painter" of Poland.
Stanisław Wyspiański has made a parody of this painting in 1904
Oof. I'm guessing he thought the original was too busy, visually.