The Battle of Eckmühl fought on 21 April – 22 April 1809, was the turning point of the 1809 Campaign, also known as the War of the Fifth Coalition.
Napoleon I had been unprepared for the start of hostilities on 10 April 1809, by the Austrians under the Archduke Charles of Austria and for the first time since assuming the French Imperial Crown had been forced to cede the strategic initiative to an opponent.
Thanks to the dogged defense waged by the III Corps, commanded by Marshal Davout, and the Bavarian VII Corps, commanded by Marshal Lefebvre, Napoleon was able to defeat the principal Austrian army and wrest the strategic initiative for the remainder of the war.
Operating over a fifty-mile front, from Regensburg (Ratisbon to the French) to Pfaffenhofen (district), marked by stretches of rugged, wooded terrain, neither the French nor the Austrians had developed adequate intelligence about their opponent's strength, dispositions or intentions. Assuming that the bulk of the Austrian army was deployed so as to cover their bridgehead at Landshut and the main highway to Vienna, on 20 April 1809, Napoleon launched most of his army in an attack to the Southwest.
The resulting Battle of Abensberg was a clear, French victory, following which Napoleon ordered all but Davout's III Corps and Lefebvre’s (Bavarian) VII Corps to pursue and destroy what he thought was the remains of the Austrian Army.
The French attack, however, had only split the Austrian Army, separating its Left Wing, composed of the V Armee Korps, VI A.K. and II Reserve A.K., from the balance of the army.
Two corps, III A.K. and IV A.K., were withdrawn by Archduke Charles to the North, forming a nine-mile line from Abbach on the Danube to Eckmühl on the Grosse Laber. More importantly, unbeknownst to Napoleon, the Austrians gained a victory of their own on 20 April 1809, by surrounding and capturing the French garrison at Regensburg and its strategic bridge over the Danube.
