[1][2] Fearing the rise in the power of Napoleon's First French Empire after their defeat of Austria and establishment of the French-sponsored Confederation of the Rhine, Prussia and Russia mobilized for a fresh campaign, and Prussian troops massed in Saxony as a part of the War of the Fourth Coalition.

The twin battles of Jena and Auerstedt were fought on 14 October 1806 on the plateau west of the river Saale, between the Grande Armée and the forces of Frederick William III of Prussia.

Karl August, Duke of Saxe-Weimar and Saxe-Eisenach, waited near Erfurt in the hope that large numbers of troops would join the retreat; when few did so, he withdrew toward Langensalza.

[4] Without support from Prussian Generalfeldmarschall Möllendorf, collapsed from injuries suffered at Auerstedt, the fortress commandant signed articles of capitulation; included in the terms were the surrender of the Petersberg Citadel and large quantities of gunpowder and munitions.

[5] Historian Francis Loraine Petre remarked that Erfurt was the first of a series of "pusillanimous capitulations" by Prussian fortress commanders, writing that Napoleon's plans might have been delayed had the city held out for just a few days.

[7] Between 27 September and 14 October 1808, Napoleon hosted the Congress of Erfurt in the principality, intended to reaffirm the alliance with the Tsar, which had been concluded the previous year with the Treaties of Tilsit at the end of the War of the Fourth Coalition.

[11] In 1811, to commemorate the birth of the Prince Imperial (later Napoleon II), a 70-foot (21-metre) ceremonial column (Die Napoleonsäule) of wood and plaster was erected on the common, on the instigation of the French administration and funded by the city treasury.

[7][12][13] Similarly, the Napoleonshöhe — a Greek-style temple topped by a winged victory with shield, sword and lance and containing a bust of Napoleon sculpted by Friedrich Döll[7][12][14] — was erected in the Stiegerwald woods on the direction of the senate-president von Resch; the design included a grotto with fountain and flower beds, using a large water basin removed from the Peterskirche.

[7][18] Coalition shelling of the Petersberg Citadel on 6 November caused substantial damage to districts to the north of the cathedral and the destruction of much of the monastery buildings and the Peterskirche.