Erfurt became part of the Kingdom of Prussia in 1802 , to compensate for territories Prussia lost to France on the Left Bank of the Rhine . In the Capitulation of Erfurt the city , its 12,000 Prussian and Saxon defenders under William VI , Prince of Orange-Nassau , 65 artillery pieces , and the Petersberg Citadel and Cyriaksburg Citadel Cyriaksburg were handed over to the French on 16 October 1806 ; At the time of the capitulation , Joachim Murat , Marshal of France , had about 16,000 troops near Erfurt . With the attachment of the Saxe-Weimar territory of Blankenhain , the city became part of the First French Empire in 1806 as the Principality of Erfurt , directly subordinate to Napoleon as an " imperial state domain " ( ) , separate from the Confederation of the Rhine , which the surrounding Thuringian states had joined . Erfurt was administered by a civilian and military Senate ( '' '' ) under a French governor , based in the , previously the seat of city 's governor under the Electorate . Napoleon first visited the principality on 23 July 1807 , inspecting the citadels and fortifications . In 1808 , the Congress of Erfurt was held with Napoleon and Alexander I of Russia visiting the city
Congress of Erfurt
Congress of Erfurt
Erfurt