Prince William was the fourth and youngest son of King Frederick William II of Prussia and Princess Frederika Louisa of Hesse-Darmstadt . He served in the Guards from 1799 and fought in 1806 at the head of a cavalry brigade at Battle of Jena and Auerstedt . In December 1807 , he traveled to Paris , to try to reduce the war burdens imposed on Prussia by Napoléon Bonaparte ; he only managed to obtain a modest reduction . In 1808 , he represented Prussia at the Congress of Erfurt . At the end of 1808 , he accompanied his brother , King Frederick William III to St. Petersburg . Later , he had a prominent role in the transformation of Prussia and its army
Congress of Erfurt
Congress of Erfurt
Prince Wilhelm of Prussia (1783–1851)