The battle of Landshut (21 April 1809) saw the French force their way across the River Isar, completing the defeat of the left wing of the Austrian army that began on the previous day at Abensberg.
Napoleon's counterattack began on 20 April (battle of Abensberg). By the end of the day the Austrian army had been split in two, with the left, under Feldmarschalleutnant Johann Freiherr von Hiller, retreating to Landshut, while the left, under the commander in chief, Archduke Charles, was left isolated in the area south of Regensburg.
Fortunately for the Archduke Napoleon believed that Hiller's force was the main Austrian force. Leaving Davout to deal with what he believed was the shattered remnants of the Austrian right, Napoleon led the rest of his army towards Landshut.
Vandamme's corps had been first to move, and it was his cavalry that first clashed with the Austrians around Landshut, taking part in a massive cavalry battle on the plains to the north of the River Isar.
Landshut, on the south bank of the Isar, was linked to the north bank by two bridges, the Lendbrücke to the west and the Spitalbrücke to the east. The latter bridge connected Landshut to the suburb of Zwischen den Brücken.
Vandamme was followed by the first infantry units of Lannes's provisional corps, the 13th Léger and 17th Ligne. They became involved in a fight with the Austrians defending Zwischen den Brücken, but before they could attack the Spitalbrücke the Austrians withdrew. An attempt to set the bridge on fire was only partly successful - most of the pioneers involved were captured, and the wet weather meant that the fires set by the remaining men didn't take hold fast enough.
By this point Napoleon had reached Landshut. Determined not to be delayed, he ordered General Georges Mouton, a member of his staff, to lead an assault across the bridge. Mouton took the grenadiers from the III/17th Ligne, ordered them not to fire their muskets, and led them across the smouldering bridge in a scene later commemorated in a famous painting. Mouton's men successfully crossed the bridge and broke through the gate guarding the town. The 13th Léger came next, followed by two squadrons of Bavarian cavalry, three battalions of Bavarian infantry and two companies from Württemberg. The attack across the bridge was made at 12.30, and by 1pm the town was in Allied hands.
Further to the west the leading elements of Massena's corps, which been sent east towards Landshut on the previous day, had crossed the Isar at Moosburg at around 10am. After that their progress had rather slowed down, and so they didn't reach the Landshut area until around 1pm, just as the town fell into French hands.
Massena arrived too late to trap Hiller at Landshut, but his men did increase the pressure on the Austrian retreat. Despite this extra pressure the Austrian rearguard, under Radetzky, managed to hold off the French, and once the Austrians reached Geisenhausen, around five miles to the south-east of Landshut, the pursuit slackened. Even then the Austrian commanders were unable to restore order, and the retreat continued until they reached Neumarkt an der Rott (now Neumarkt-Sankt Veit). The retreat and fighting at Landshut cost the Austrian left wing around 8,000 men, while the French and Allied losses were fewer than 1,000. The French also captured large quantities of supplies, most abandoned to the north of the river.
That night Napoleon's army camped around Landshut, but it was now becoming clear that Napoleon had not been chasing the main part of the Austrian army. Further to the north Davout's corps found itself facing the three intact corps still under the command of Archduke Charles. On the following day Napoleon was forced to turn north to fight the battle of Eggmühl.