Battle of Heilsberg The Battle of Heilsberg took place on 10 June 1807 , during the Napoleonic Wars . Overview . On 24 May 1807 , the Siege of Danzig ended when Prussian General Friedrich Adolf , Count von Kalckreuth capitulated to French Marshal Francois Joseph Lefebvre . With Gdansk ( Danzig ) secured , Napoleon was now free to turn against Bennigsen ' s army . Yet it was the Russian who struck first when he ordered his columns to converge on Marshal Michel Ney ' s exposed VI Corps on 2 June . Outnumbered 63 , 000 to 17 , 000 , Ney fought a brilliant rear guard action at the Battle of Guttstadt - Deppen on 5 and 6 June . Though he lost his baggage train , two guns , and 2 , 042 men , Ney managed to escape to the southwest over the Pasłęka ( Passarge ) River with the bulk of his soldiers , leaving Bennigsen seething with rage over his missed opportunity . Within two days , Napoleon ordered his 190 , 000 - man army to close in on the 100 , 000 Russians and 15 , 000 Prussians . Detecting the approaching avalanche , Bennigsen ordered his troops to retreat on Lidzbark Warmiński ( Heilsberg ) . The Russian army took up strong defensive positions around the town , which stood on the Łyna ( Alle ) River . The French army , under Marshals Murat and Lannes , attacked on 10 June . Bennigsen repelled several attacks , resulting in huge French casualties , but had to withdraw towards Friedland the following day . Four days later , the decisive Battle of Friedland occurred , ending the War of the Fourth Coalition with the passing of the Treaty of Tilsit . Influences on the battle . Geography The Battle of Heilsberg was fought on the Alle river , known today as the Lyna . The Teutonic Castle being the focal point of the battle was held by Russian control . Terrain Aside from geographical advantages , the Russians had also spent three to four months compiling tactics on how to defend against a French invasion , regardless of where they would attack the castlegrounds . Defensively , the castle was supported by its bridges and walls , both of which were built along the perimeter of the castle . The land surrounding the Teutonic Castle acted as an obstacle for the French army due to the increase of elevation from the base of the river to the castles foundation . Climate Although the terrain was punishment enough for the French , weather also took a toll on their abilities and health . During the day , on top of the weight being carried in regards to supplies and armory , temperatures reached dangerously hot and humid levels . The dampness and bitter cold of the night also played a significant role by providing little opportunity for rest . Strategies and tactics . Beginnings of the battle : The French were out numbered by the Russians , and knowing this , positioned themselves to cut off any opportunity for the Russians to obtain reinforcements . At the beginning of the battle , French army men were separating amongst their own divisions . This tactic was thought to help block Russian sights in terms of all the French positioning and flanking . Although the woods surrounding the French had provided a perimeter of camouflage , the shrubbery did not extend to the barren field in front of the castle . It was because of the forest density , however , that dodging the Russian artillery and infantry fire was difficult to maneuver around . Middle / End of the battle : In the midst of war , French cavalry leaders Murat , Soult , and Lannes had segregated their troops from the greater unit , which would soon result in utter failure . After such separation , the smaller units within the reserves had refused orders to flank and attack stronger sides of the Russian armies . This was partly due to the fact that orders being issued by reserves of the secondary infantry , rather than Marshalls and Major Generals , were not given enough of credit of leadership in their absence . Despite both sides losing a significant number of men , each refused to withdrawal their armies . The realization of the large number of French soldiers who had already been a victim of death , and the success of the Russian defense gave Bennigsen and Napoleon little choice but to call an undocumented truce to end the war . This truce was signaled when both sides focused solely on the health of wounded soldiers rather than that of offensive tactics . By leaving behind weaponry as proof of their intent , medics and soldiers alike began helping those who were wounded , or retrieve the dead . Outcome and post - war analysis : This battle is recognized as having been tactically indecisive due to neither side having gained any significant ground , it is most notably discussed as a battle that yielded little change in the balance of strength between the Russians and the French . The Battle of Heilsberg was fought four days before the decisive Battle of Friedland . French Army men Accountability : 1398 killed 10 , 359 wounded 864 captured Russian Army men Accountability : 9000 killed / wounded / captured Notable officers of the French Army present were : Notable officers of the Russian Army present were :