The battle of St. Michael (25 May 1809) was a disastrous Austrian defeat that saw an entire division destroyed, dramatically reducing their ability to defend against a French invasion from Italy. The battle was an almost accidental clash between forces from separate theatres of the war. Prince Eugène began the war in northern Italy, facing an Austrian invasion across the Alps, while Feldmarschalleutnant Franz Jellacic Freiherr von Buzim had been involved in the Austrian invasion of Germany, and had been separated from the main army after Napoleon's early victories. He moved into the Tyrol before being ordered to move east to join Archduke John and the Austrian army that had been forced to retreat from Italy. By late May Jellacic's men were moving from west to east across Eugène's line of march.
The Austrian invasion of Italy had begun well, with victory at Sacile on 16 April, but the Archduke's advance had been halted by news from Germany, where Napoleon had won a series of battles, ending at Eggmuhl on 22 April. The Archduke had moved onto the defensive, but was then defeated on the Piave (8 May) and forced to retreat back into Austria. On 18 May he was defeated again at Tarvisio, and on 20 May Eugène entered Klagenfurt. From Klagenfurt the French moved north-east along the Mur valley, heading towards Napoleon's main army at Vienna.
St. Michael is on the north bank of the Mur, which runs west to east here. A spur of high ground connects the mountains to the river just to east of the village, while a plateau overlooks the place. Just to the west of the village the Leising River joins the Mur.
On 24 May Jellacic reached Mautern, in the Leising Valley. His scouts reported that there were French cavalry at Judenburg, to the south-west of St. Michael, but Jellacic believed that he could only be facing light troops, and so on the morning of 25 May he ordered his men to continue their march down the Leising towards St. Michael. Once in the Mur valley he intended to follow the river downstream to Leoben, before turning east to reach the Archduke at Graz.
Early on 25 May Eugène was at Unzmarkt, to the west of Judenburg. His scouts reported the presence of Jellacic's 8,000 men to the north, and Eugène decided to try and trap them at St. Michael. General Paul Grenier's 15,000 strong corps was ordered to move down the valley to intercept the Austrians.
The first clash came between the two side's advance guards at around 9am, and helped to convince Jellacic that he was only facing light troops. In fact Seras's division, with eight infantry battalions, four cavalry squadrons and ten guns, was fast approaching, and was able to occupy a dangerous position on the plateau of St. Michael, an area of higher ground that dominated the Austrian escape route.
At this stage the French were not strong enough to hold the plateau. While Oberst Ludwig Eckhardt captured a key bridge over the Leising, Generalmajor Ettingshausen, with the Austrian right, drove Seras off the plateau.
The Austrian line now ran for a mile across the valley. The Grenzers and Landwehr were on the right, reaching as far as the wooded Fresenberg hill. Generalmajor Ignaz Freiherr von Legisfeld commanded two and a half battalions in the Austrian centre, on the plateau of St. Michael, while General Ettingshausen now commanded the left, which stretched down to the Mur. For the moment the French were outnumbered, and so Seras restricted himself to an exchange of cannon fire.
In the early part of the afternoon General Pierre Durutte arrived on the scene with the rest of Grenier's corps, and the French now outnumbered the Austrians. Seras began with an attack on the Austrian flanks - two battalions attacked their left, six their right and two the Austrian rear. This attack must have been repulsed, for at about 4pm Prince Eugène ordered Seras to attack the Austrian centre with six battalions, with another eight battalions close behind and the French cavalry in support.
This attack finally broke the Austrian line. The cavalry reached the key river bridges, and after ten minutes of fighting the Austrian infantry broke and fled. In the pursuit that followed around 4,000 Austrians were taken prisoner, and only 2,000 men escaped to reach Archduke John at Graz. French casualties were much lower.
In the aftermath of this battle Prince Eugène continued towards Vienna to join Napoleon. Archduke John was forced to abandon Graz by General Macdonald, with Eugène's right wing, which had been detached to march through Trieste and Laybach (Ljubljana). The Archduke retreated towards Raab, where he would suffer another defeat on 14 June.