Clouds of war between Prussia and Napoleonic France had been gathering since August 1806 . By October 1806, the main belligerents, the Prussian Army and Napoleon’s Grande Armee, had concentrated in southern Germany, separated by the Thuringian Forest. Following minor clashes with Prussian detachments at Schleiz and Saalfeld, Napoleon pushed on eastwards, hoping to catch the main Prussian force which he suspected were based at nearby Jena. By the time the French reached Jena on 13th October 1806, most of Prussian army was already retreating towards Auerstedt (sometimes spelled Auerstädt or Auerstaedt).  Meanwhile, Prussian-Saxon allied forces had been gathering west of Jena with the aim of securing the Prussian retreat. Two battles took place, both ending in French victories and a decisive defeat of the bulk of the Prussian army.