Free Imperial City of Nuremberg
The Free Imperial City of Nuremberg (German: Freie Reichsstadt Nürnberg) was a free imperial city – independent city-state – within the Holy Roman Empire. After Nuremberg gained piecemeal independence from the Burgraviate of Nuremberg in the High Middle Ages and considerable territory from Bavaria in the Landshut War of Succession, it grew to become one of the largest and most important Imperial cities, the 'unofficial capital' of the Empire, particularly because numerous Imperial Diets (Reichstage) and courts met at Nuremberg Castle between 1211 and 1543.
Source: Wikipedia — Free Imperial City of Nuremberg (CC BY-SA 4.0)