The combat of Giessen (16 September 1796) was a diversionary Austrian attack on the left wing of the French position on the Lahn that helped the Archduke Charles fight his way across that river further to the west, at Limburg.
After his defeat at Würzburg on 3 September General Jourdan had been forced to retreat north-west across the foothills of the Vogelsberg. On 9 September the French reached the River Lahn, where on the following day they were joined by 16,000 fresh troops under General Marceau, who had been forced to abandon his blockade of Mainz. Jourdan decided to defend the line of the Lahn in the hope that this would prevent the Archduke from turning south to defeat General Moreau's army in southern Germany.
In that respect at least Jourdan was successful. After stopping at Würzburg for long enough to capture the citadel, the Archduke followed him north to the Lahn, reaching that river on 11 September. The Archduke decided to make his main attack against the French centre-right at Limburg, but to attempt to convince Jourdan that he was actually going to attack the French left, at Giessen and Wetlzar.
Over the next few days the Austrians thoroughly convinced Jourdan of this, and by the end of 15 September the French were concentrated on their left. Marceau was posted between the Rhine and Limburg, with his advance guard at Mensfelden, 3-4 miles south-east of the town. Bernadotte was five miles to the east, at Runkel, Championnet was six miles further to the north-east, at Weilburg, Lefebvre was at Wetzlar and Grenier was at Giessen.
In contrast the main Austrian forces, under the Archduke Charles, were posted at Niederbrechen, five miles east of Limburg. Neu's division was at Kirchberg and Hotze was at Weilmünster (ten miles to the east of the Archduke). Kray and Sztaray had been left opposite Giessen and Wetzlar, with orders to make a noisy demonstration that would convince the French that they were the main force.
Part of Grenier's division was posted around Giessen, on the left bank of the Lahn. Kray decided to attack the left flank of these forces, taking advantage of cover provided by the wood of Lollar, just to the north. This attack pushed back Grenier's outposts, and forced Olivier's brigade off the heights in front of the town.
Jourdan sent Bonnaud's cavalry, a demi-brigade of infantry, a regiment of cuirassiers and a light artillery battery to help Grenier. The Austrians also fed reinforcements into the fight, but eventually the French forced them to retreat from the river.
Kray responded to this by launching a new attack on Grenier's right at Giessen. Grenier's right-hand brigade was forced to retreat. Bonnaud, taking advantage of a ravine between the two forces, led two cavalry squadrons around the fighting and attacked the Austrian column from its left. Seeing that the Austrians were under pressure Generals Leval and Olivier ordered their infantry to charge, and the Austrians were repulsed. During this fighting General Bonnaud's thigh was broken by a musket ball, and he died a few months later.
The attack at Giessen achieved its main aim. Jourdan was distracted from the more important fighting going on to the west at Limburg, and the Archduke was able to break through the French lines. Jourdan was forced to retreat once again, losing a third battle at Altenkirchen on 19 September before retreating back across the Rhine.