Napoleon did not hear of it before August 16th, and it was not until a week later that he realized how vast were the forces that would threaten his rear.

For the present his plan was to hold the Bohemian passes south of Bautzen and Pirna, so as to hinder any invasion of Saxony, while he threw himself in great force on the Army of Silesia, now 95,000 strong, though he believed it to number only 50,000.[345] While he was crushing Bluecher, his lieutenants, Oudinot, Reynier, and Bertrand, were charged to drive Bernadotte's scattered corps from Berlin; whereupon Davoust was to cut him off from the sea and relieve the French garrisons at Stettin and Kuestrin.

Thus Napoleon proposed to act on the offensive in the open country towards Berlin and in Silesia, remaining at first on the defensive at Dresden and in the Lusatian mountains.

This was against the advice of Marmont, who urged him to strike first at Prague, and not to intrust his lieutenants with great undertakings far away from Dresden.

The advice proved to be sound; but it seems certain that Napoleon intended to open the campaign by a mighty blow dealt at Bluecher, and then to lead a great force through the Lusatian defiles into Bohemia and drive the allies before him towards Vienna.
But what did he presume that the allied forces in Bohemia would be doing while he overwhelmed Bluecher in Silesia?
Would not Dresden and his communications with France be left open to their blows?
He decided to run this risk.