At the Battle of Friedland, Andrew Roberts explains (in Napoleon: A Life), the French obtained a decisive victory and routed much of the Russian army:
When Ney’s exhausted corps began to fall back, Sénarmont divided his thirty guns into two batteries of fifteen each, with 300 rounds per cannon and 220 per howitzer. Sounding ‘Action Front’ on his bugles, his teams galloped forward, unlimbered and fired first at 600 yards, then at 300, then at 150, and finally, with nothing but canister-shot, at 60. The Russian Ismailovsky Guards and the Pavlovsky Grenadiers tried to attack the batteries, but some 4,000 men fell to their fire in about twenty-five minutes. An entire cavalry charge was destroyed with two volleys of canister. The Russian left was utterly destroyed, and trapped against the Alle river. Sénarmont’s action became famous in military textbooks as an ‘artillery charge’, although his gunners suffered 50 per cent casualties.
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Heat, exhaustion, nightfall and the pillaging of the town for food have all been advanced as explanations for why there was no Jena-style pursuit of the Russians after Friedland. It is also possible that Napoleon felt a wholesale massacre might have made it harder for Alexander to come to terms, and by then he very much wanted peace.
‘Their soldiers in general are good,’ he told Cambacérès, something he had hitherto not recognized, and which he would have done well to remember five years later.
For sheer concentration of effort, Friedland was Napoleon’s most impressive victory after Austerlitz and Ulm. At the cost of 11,500 killed, wounded and missing, he had utterly routed the Russians, whose losses have been estimated at around 20,000–or 43 per cent of their total–though only around twenty guns.
Percy’s hundred surgeons had to work through the night, and a general later recalled ‘meadows covered with limbs severed from their bodies, those frightful places of mutilation and dissection which the army called ambulances’.