The Battle of Abensberg took place on 20 April 1809 between a Franco-German force under the command of Emperor Napoleon I of France and a reinforced Austrian corps led by Feldmarschall-Leutnant Archduke Louis of Austria. As the day wore on, Feldmarschall-Leutnant Johann von Hiller arrived with reinforcements to take command of the three corps that formed the Austrian left wing. The action ended in a complete Franco-German victory. The battlefield was southeast of Abensberg and included clashes at Offenstetten, Biburg-Siegenburg, Rohr in Niederbayern, and Rottenburg an der Laaber. On the same day, the French garrison of Regensburg capitulated. After Marshal Louis-Nicolas Davout's hard-fought victory at Battle of Teugen-Hausen the previous day, Napoleon determined to break through the Austrian defenses behind the Abens River. The emperor assembled a provisional corps consisting of part of Davout's corps plus cavalry and gave Marshal Jean Lannes command over it. Napoleon directed his German allies from the Kingdom of Bavaria and the Kingdom of Württemberg to attack across the Abens from the west, while Lannes thrust from the north toward Rohr. While the Austrians initially held the river line, Lannes' strike force crashed through Louis' defenses farther east. On the left, the Austrians managed to conduct a capable rear guard action, but during the day the French smashed their opponents' right flank and captured thousands of soldiers. The day ended with the Austrians barely holding onto a line behind the Große Laber River. The next day, Hiller withdrew to Landshut, separating the left wing from the main army under Generalissimo Archduke Charles, Duke of Teschen near Regensburg (Ratisbon). The French surrender of Regensburg on 20 April allowed Charles' army a retreat route to the north bank of the Danube. The Battle of Landshut was fought on 21 April. Background Operations Archduke Charles stole a march on Napoleon when his army invaded the Kingdom of Bavaria on 10 April 1809. Even though the Austrian army took six days to slowly march from the Inn River at the frontier to the Isar River, the move placed the army of France and their German allies in grave danger. Napoleon's deputy commander Marshal Louis Alexandre Berthier mismanaged the Grande Armée's concentration, leaving its units scattered across a broad front in a confused state. The central mass of Archduke Charles' 209,600-man host crossed the Isar at Landshut on 16 April, but the next day Emperor Napoleon arrived at the front