The Fourth Coalition fought against Napoleon's French Empire and were defeated in a war spanning 1806–1807. The main coalition partners were Prussia and Russia with Saxony, Sweden, and Great Britain also contributing. Excluding Prussia, some members of the coalition had previously been fighting France as part of the Third Coalition, and there was no intervening period of general peace. On 9 October 1806, Prussia joined a renewed coalition, fearing the rise in French power after the defeat of Austria and establishment of the French-sponsored Confederation of the Rhine. Prussia and Russia mobilized for a fresh campaign with Prussia massing troops in Saxony.
Napoleon decisively defeated the Prussians in an expeditious campaign that culminated at the Battle of Jena–Auerstedt on 14 October 1806. French forces under Napoleon occupied Prussia, pursued the remnants of the shattered Prussian Army, and captured Berlin. They then advanced all the way to East Prussia, Poland and the Russian frontier, where they fought an inconclusive battle against the Russians at the Battle of Eylau on 7–8 February 1807.