Karl Theodor Anton Maria von Dalberg (8 February 1744 – 10 February 1817) was a Catholic German bishop and statesman. In various capacities, he served as Archbishop of Mainz, Prince of Regensburg, Arch-Chancellor of the Holy Roman Empire, Bishop of Constance and Worms, Prince-Primate of the Confederation of the Rhine and Grand Duke of Frankfurt. Dalberg was the last Archbishop-Elector of Mainz.
Frankfurt was a major city of the Holy Roman Empire, being the seat of imperial elections since 885 and the city for imperial coronations from 1562 (previously in Free Imperial City of Aachen) until 1792. Frankfurt was declared an Imperial Free City (Freie und Reichsstadt) in 1372, making the city an entity of Imperial immediacy, meaning immediately subordinate to the Holy Roman Emperor and not to a regional ruler or a local nobleman.
Due to its imperial significance, Frankfurt survived mediatisation in 1803. Following the collapse of the Holy Roman Empire in 1806, Frankfurt fell to the rule of Napoleon I, who granted the city to Karl Theodor Anton Maria von Dalberg; the city became known as the Principality of Frankfurt. The Catholic cleric Dalberg emancipated Catholics living with the city boundary. In 1810 Dalberg merged Frankfurt with the Principality of Aschaffenburg, the County of Wetzlar, Fulda, and Hanau to form the Grand Duchy of Frankfurt. After the defeat of Napoleon and the collapse of the Confederation of the Rhine, Frankfurt was returned to its pre-Napoleonic constitution via the Congress of Vienna of 1815 and became a sovereign city-state and a member of the German Confederation.
The Principality of Aschaffenburg (German: Fürstentum Aschaffenburg) was a principality of the Holy Roman Empire created in 1803 and, following the dissolution of the Empire in 1806, of the Confederation of the Rhine, which existed from 1806 to 1810. Its capital was Aschaffenburg.
With the secularization of the Archbishopric of Mainz in 1803, Karl Theodor Anton Maria von Dalberg was compensated by receiving the newly created principalities of Aschaffenburg and Regensburg and the County of Wetzlar. Along with the city of Aschaffenburg, the Principality of Aschaffenburg also consisted of Klingenberg, Lohr, Aufenau, Stadtprozelten, Orb, and Aura.