The Battle of Sempach was fought on July 9, 1386, between Leopold III, Duke of Austria, and the Old Swiss Confederacy.
The Confederation army had presumably assembled at the bridge over the Reuss River at Gisikon. It marched from there, hoping to catch Leopold still at Sempach where he could be pressed against the lake. Around noon, the two armies made contact about 2 km outside of Sempach. This was to the mutual surprise of both armies, which were both on the move and not in battle order. But both sides were willing to engage and formed ranks. The site of the battle is marked by the old battle chapel, which was originally consecrated in the year after the battle.