Battle of Wilkomierz The Battle of Wilkomierz ( also called the " Battle of Vilkomir " , " Ukmergė " , " Pabaiskas " , " Swienta " or " Šventoji " ) took place on September 1 , 1435 near Ukmergė ( Polish : " Wiłkomierz " ) , by the Šventoji River in the Grand Duchy of Lithuania . The word " pabaiskas " is a Lithuanization of the Polish word " pobojowisko " , meaning " battle site " and did not come into use until after the battle itself . With the help of military units from the Kingdom of Poland , the forces of Grand Duke Sigismund Kęstutaitis soundly defeated Švitrigaila and his Livonian allies . The battle ended the Lithuanian Civil War ( 1431 – 1435 ) and inflicted major damage to the Livonian Order . Background . In 1430 Vytautas the Great died without an heir . The Lithuanian nobles elected Švitrigaila , Jogaila ' s brother and Vytautas ' cousin , as the new Grand Duke without consulting with Poland . This violated the Union of Horodło of 1413 , and outraged the Polish nobles . Švitrigaila prepared for war and enlisted the Teutonic Knights , Moldavia , and the Golden Horde as his allies . Sigismund Kęstutaitis assumed power in Lithuania when he deposed Švitrigaila in a coup on August 31 , 1432 . Švitrigaila escaped , established himself in Polotsk , and rallied his supporters from Slavic lands of the Grand Duchy against Sigismund . The Teutonic Knights secretly supported Švitrigaila chiefly through its branch in Livonia . Švitrigaila and Sigismund were now engaged in a destructive civil war . In December 1432 their armies fought in the Battle of Ašmena ; Švitrigaila was defeated , but the victory was not decisive . In 1433 together with the Livonian knights , Švitrigaila raided Lida , Kreva , Eišiškės and devastated the surrounding areas near Vilnius , Trakai , and Kaunas . After Jogaila ' s death in 1434 , the Teutonic Knights resumed their war against Poland . Battle . Each side mobilized around 15 , 000 troops ( in some cases estimates run up to 30 , 000 on each side ) . Švitrigaila commanded forces of Lithuanians , Orthodox Ruthenians , Livonian Knights , at least 500 Tatars from the Golden Horde , and a few Teutonic Knights . There might have been some Hussite s on his side as he enlisted his nephew Sigismund Korybut , a distinguished military leader during the Hussite Wars . Sigismund Kęstutaitis commanded Lithuanian and Polish army ( Poland army had about 8 , 000 troops ) . His son Michael commanded Samogitian troops and Jakub Kobylański was in charge of Polish forces . The opponents met about south of Vilkmergė near the Šventoji River . Later a town , named Pabaiskas , was built in the field to commemorate the battle . At first the armies were separated by the Lake Žirnajai and a marshy creek . The armies could not engage each other . After two days Švitrigaila and Livonian Grand Master Franco Kerskorff decided to change their position and move towards Vilkmergė . As the army marched , it was attacked by Sigismund Kęstutaitis , split in half and soundly defeated . Švitrigaila escaped to Polotsk with about 30 followers . Kerskorff was killed in the battle . Korybut was severely wounded and captured . He died few days later ; historians speculate whether he died of the wounds , was drowned , or poisoned . Aftermath . The battle reduced the power of the Livonian Order as its army was defeated , Grand Master killed , and many senior officers taken prisoners . The damage to the Livonian Order caused by the battle is often compared to the consequences that the Battle of Grunwald ( 1410 ) had on the Teutonic Knights . The peace treaty was signed on December 31 , 1435 in Brześć Kujawski . The Teutonic and Livonian Orders promised not to interfere with internal matters of Lithuania or Poland . Even Pope or Holy Roman Emperor could not force the Orders to violate the treaty . The peace did not alter borders established in the Treaty of Melno ( 1422 ) . Livonian Order ' s defeat in the battle brought it closer to its neighbors in Livonia . The Livonian Confederation agreement was signed on December 4 , 1435 by the Livonian Order , Livonian Bishops , vassals and city representatives . Švitrigaila escaped and continued to resist , but he was losing his power in the eastern provinces of the Grand Duchy of Lithuania . In 1437 , he proposed a compromise : he would continue to rule Kiev and Volhynia , territories that still remained loyal to him , in exchange for peace and promise to transfer these lands after his death to the King of Poland . Because of strong protests from Sigismund Kęstutatis , the Polish Senate did not ratify the agreement . The following year Švitrigaila retreated to Moldavia . Sigismund became the undisputed Grand Duke of Lithuania . However , his reign was short as he was assassinated in 1440 . A church was built in the battlefield by Sigismund Kęstutaitis to commemorate his victory . The town of Pabaiskas later grew around the church .