During the Napoleonic Wars Hamburg was occupied by France from 1806 and annexed into the Bouches-de-l'Elbe département of the First French Empire in 1811. The French government promoted the French language and instituted numerous changes in Hamburg. In February 1813 Seyler was appointed by the French authorities as a deputy judge on the commercial tribunal (tribunal de commerce). During the spring of 1813 he was among 30 prominent and wealthy Hamburg merchants who were briefly held as hostages by the French authorities to force the city to pay a "contribution" to the French government, which caused great consternation in Hamburg.
