The Battle of Sempach was fought on July 9, 1386 between Duke Leopold III of Austria and the Swiss Confederation.

Duke Leopold III, after he unsuccessfully tried to establish a cheap peace, decided to assemble his forces in order to save possessions and honor of his house. With the help from Tyrol and Italy his army was considerably stronger than that of his uncle Leopold I of Austria at Morgarten . His strength was estimated to be between 3000 and 4000 men.

But the Confederation's army was also probably twice as strong as at the Battle of Morgarten and numbered somewhere between 6000 and 8000 men, since it was made not only of men from the four forest cantons, but also other Swiss cantons (Lucerne, Zürich).

Leopold wisely decided not to attack principal places and turned to the small town of Sempach, some 9 to 10 miles north of Lucerne. He assembled his army at Sursee , about 5 miles down from Sempach, surrounded Sempach and on the same day started to march towards the expected relief army. He did not take the direct route to Lucerne, but rather turned east. He must have known that an enemy army was approaching from there.

The Confederation army had presumably assembled at the bridge over the Reuss River at Gislikon . 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 near Sempach, close to the village of Hildisrieden . The battlefield has definitely proven to be by the old battle chapel.

As the knights of Leopold's army approached, they dismounted and sought to storm the high ground. Their marksmen then took the Swiss under heavy fire. Leopold reasonably believed that the Swiss army lay before him, and engaged in battle before his rear units moved up from the approaching column. But it was only the confederate's advance guard that they were fighting.

The main body of the Confederation army finally completed its deployment from the marching column, formed up, and attacked the knights from the flank aggressively. The attack was so powerful that the knights fighting on foot were immediately overrun and the soldiers, who were holding knights' horses, took flight and the mounted Habsburg army was carried away by the fugitives.

Duke Leopold and with him a large number of nobles and knights were slain.

(after Delbrück, Medieval Warfare, Univ. of Nebraska Press 1990)