Upon Napoleon's annexation of the Papal States the following year, Roederer was appointed Prefect of the newly created Department of Trasimène, under which name Umbria had been incorporated into the French Empire. The name derived from Lake Trasimene, the fourth largest in Italy, which lay the centre of the province, and which the classically-minded Napoleon would doubtless have known from the famous Battle of Lake Trasimene in 217BC, at which Hannibal had decisively defeated the forces of the Roman Republic. Taking up his post in Spoleto on 6 September 1809, Roederer governed Trasimène loyally until its dissolution upon the fall of Napoleon in 1814, when the territory was returned to the restored Papal States.