The twin battles of Jena and Auerstedt were fought on 14 October 1806 on the plateau west of the river Saale in today's Germany, more specifically in today's Thuringia, between the forces of Napoleon I of France and Frederick William III of Prussia, at the outset of the War of the Fourth Coalition during the Napoleonic Wars. The disastrous defeats suffered in these battles by the Prussian Army, which had not been reformed for about half a century, subjugated the Kingdom of Prussia to the French Empire until the Sixth Coalition was formed in 1813.