The Union of Horodło or Pact of Horodło was a set of three acts signed in the town of Horodło on 2 October 1413. The first act was signed by Władysław II Jagiełło, King of Poland, and Vytautas, Grand
Mound of the Horodło Union; the monument was built in 1861 in Horodło to celebrate the 448th anniversary of the union.