Fearing the rise in the power of Napoleon's First French Empire after their defeat of Austria and establishment of the French-sponsored Confederation of the Rhine, Prussia and Russia mobilized for a fresh campaign, and Prussian troops massed in Saxony as a part of the War of the Fourth Coalition. The twin battles of Jena and Auerstedt were fought on 14 October 1806 on the plateau west of the river Saale, between the and the forces of Frederick William III of Prussia. The decisive defeat suffered by the Prussian Army subjugated Prussia to the French Empire until the Sixth Coalition was formed in 1813.&lt;ref name="Chandler 1966/2009"&gt;&lt;/ref&gt;