Political map of Europe & the Mediterranean 20 September 1870 (Siege of Paris): With the French defeat at Sedan (Battle of Sedan (1870)), Napoleon III was forced to surrender. The Prussians now moved to besiege Paris (Siege of Paris (1870%E2%80%931871)), where the Empire (Second French Empire) had been overthrown and a republic (French Third Republic) declared. Meanwhile the Italians took advantage of the French defeat to seize Rome (Capture of Rome).