As winter broke in 1799, on 1 March, General
Jean Baptiste Jourdan and his army of 25,000, the so-called Army of Observation, crossed the
Rhine between
Basel and
Kehl. This crossing officially violated the
Treaty of Campo Formio. On 2 March, the Army was renamed
Army of the Danube, upon orders of the
French Directory. The Army met little resistance as it advanced through the Black Forest in four columns, through the Höllental (Hölle valley), via
Oberkirch, and
Freudenstadt, and at the southern end of the forest, along the Rhine bank. Although prudent counsel might have advised Jourdan to establish a position on the eastern slope of the mountains, he did not; instead he pushed across the Danube plain, taking position between
Rottweil and
Tuttlingen. The Austrian Army and Archduke Charles, its commander-in-chief, had wintered with his army in the Bavarian, Austrian, and Salzburg territories on the eastern side of the Lech; his force alone numbered close to 80,000 troops, and outnumbered the French force by three to one. An additional 26,000, commanded by
Friedrich Freiherr von Hotze, guarded the
Vorarlberg, and further south, another 46,000, under command of
Count Heinrich von Bellegarde, formed the defense of the
Tyrol. The Austrians had already reached an agreement with
Tsar Paul of Russia by which the legendary
Alexander Suvorov would leave retirement to assist Austria in Italy with another 60,000 troops.
Engagement at Ostrach The Army of the Danube advanced on Pfullendorf and Ostrach, the former an imperial city in Upper (southern)
Swabia, and the latter a nearby village of 300 belonging to the
Imperial Abbey of Salem, an influential and wealthy ecclesiastical territory on Lake Constance. Jourdan's objective was simple and direct: cut the Austrian line at the border of the southwestern German states and Switzerland, preventing the Coalition's use of Switzerland as an overland route between central and southern Europe. Isolation of the two theaters would prevent the Austrians from assisting one another; furthermore, if the French held the interior passes in Switzerland, they could use these routes to move their own forces between the two theaters. Stretching between the Pfullendorf heights and the village lies a flat, wide plain, marshy in places, ringed with low-lying hills, and creased with a small tributary stream from which the village takes its name. Ostrach itself lies almost at the northern end of this plain, but slightly south of the Danube itself. By 7 March, the first French forces arrived there, and the Austrians arrived a day or so later. Over the following week, additional forces for both sides arrived, and the two armies faced each other across this valley. The French army extended in a long line from the Danube to Lake Constance. The Third Division, commanded by
Laurent de Gouvion Saint-Cyr, positioned itself at the far left flank, and
Dominique Vandamme's detached force, returning from reconnaissance near Stuttgart, roamed on the north shore of the river.
François Joseph Lefebvre commanded the Advance Guard, positioned on the slope below Pfullendorf, and
Joseph Souham, with the Second Division, took position behind him.
Pierre Marie Barthélemy Ferino's First Division held the southernmost flank, to defend against any encirclement by Charles' force. Jourdan set up command at Pfullendorf, and the Cavalry Reserve, commanded by
Jean-Joseph Ange d'Hautpoul, stood slightly to the north and west of Souham. By late on the 19th, Austrian and French soldiers had been skirmishing at outposts for more than 30 hours, with the action growing increasingly intense. In the early hours of the 21st, General Lefebvre informed Jourdan that the Austrians were attacking all his positions, and that the general engagement would begin shortly. After 24 hours of fighting, Austrian forces pushed Lefebvre and Saint Cyr's troops back to the Pfullendorf heights. Although sappers blew up the primary bridge over the
Ostrach river, the Austrians managed to ford the stream anyway. They nearly outflanked General Saint Cyr's forces on the right flank, did outflank Lefebvre's forces in the center, and cut off a portion of the southern flank from the main body. Saint Cyr's troops barely managed to pull back before being fully cut off. Finally, General
Friedrich Freiherr von Hotze, marching north with 10,000 men, from
Feldkirch, threatened Ferino's First Division from the south.
Retreat from Ostrach On 21 March, at 2200, Jourdan ordered the wounded to be transported to
Schaffhausen in Switzerland, via Stockach. The main army then began its own retreat in the early morning of the 22nd. The reserve division of d'Hautpoul left first, and pulled back via Stockach to Emmengen ob Eck. The first division pulled back to Bodman, on the northern tip of the Überlingen-finger of Lake Constance; in the retreat, a portion of the force was encircled and cut off by the 2nd Lancers of
Karl Philipp, Prince Schwarzenberg's brigade, and more than 500 were taken prisoner. ==Battle at Stockach and Engen==