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 Hussites 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 9 km 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.