 It was used as a palace by Napoleon during all of his 9 stays in Mainz, who planned to double the size of the building and use it as an imperial residence, as "Mayence" was intended to become one of the "bonnes villes de l'Empire", the 36 most important cities of France.In the aftermath of the Napoleonic Wars, the building was used by the Dukes of Hesse-Darmstadt, who obtained the territory of Mainz after the Congress of Vienna.In 1870, the building served as the headquarters of the Prussian army in the early stages of the Franco-Prussian War.