On the first of October the Prussian Minister at Paris presented a note to Talleyrand, demanding, among other things, that the formation of a Confederacy in the North of Germany should no longer be thwarted by French interference, and that the French troops within the territories of the Rhenish League should recross the Rhine into France, by the 8th of the same month of October.
But Napoleon was already in person on the German side of the Rhine; and his answer to the Prussian note was a general order to his own troops, in which he called on them to observe in what manner a German sovereign still dared to insult the soldiers of Austerlitz.
The conduct of Prussia, in thus rushing into hostilities, without waiting for the advance of the Russians, was as rash as her holding back from Austria, during the campaign of Austerlitz, had been cowardly.

As if determined to profit by no lesson, the Prussian council also directed their army to advance towards the French, instead of lying on their own frontier--a repetition of the great leading blunder of the Austrians in the preceding year.

The Prussian army accordingly invaded the Saxon provinces, and the Elector, seeing his country treated as rudely as that of Bavaria had been on a similar occasion by the Austrians, and wanting the means to withdraw his own troops as the Bavarian had succeeded in doing under like provocation, was compelled to accept the alliance which the Cabinet of Berlin urged on him, and to join his troops with those of the power by which he had been thus insulted and wronged.
No sooner did Napoleon know that the Prussians had advanced into the heart of Saxony, than he formed the plan of his campaign: and they, persisting in their advance, and taking up their position finally on the Saale, afforded him, as if studiously, the means of repeating, at their expense, the very manoeuvres which had ruined the Austrians in the preceding campaign.

In a word, he perceived that the Prussian army was extended upon too wide a line, and the consequent possibility of destroying it in detail.

He further discovered that the enemy had all his principal stores and magazines at Naumburg, to the rearward, not of his centre, but of his extreme right; and resolved to commence operations by an attempt to turn the flank, and seize those magazines, ere the main body of the Prussians, lying at Weimar, could be aware of his movement.