On his return he did not take part in the Battle of Marengo, where his friend Desaix was killed while making a decisive contribution to the victory. Napoleon, who had great confidence in his abilities, finally promoted him to general of division and arranged his marriage to his sister Pauline's sister-in-law Aimée Leclerc, thus making him part of Napoleon's extended family, and gave him a command in the consular guard. At the accession of Napoleon as emperor in 1804, Davout was named as one of the original 18 Marshals of the Empire. Davout was the youngest and least experienced of the generals promoted to marshal, which earned him the hostility of other generals throughout his career. As commander of the III Corps of the "Grande Armée", Davout rendered his greatest services. At the Battle of Austerlitz, following a forced march of 48 hours, the III Corps bore the brunt of the allies' attack. In the subsequent War of the Fourth Coalition, Davout, with a single corps, fought and won the Battle of Auerstädt against the main Prussian Army, which had more than twice as many soldiers at its disposal (more than 63,000, to Davout's 28,000). Historian François-Guy Hourtoulle writes: "At Jena, Napoleon won a battle he could not lose. At Auerstädt, Davout won a battle he could not win". As a reward, Napoleon let Davout and his men enter first in Berlin on 25 October 1806.