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.