But Napoleon once more made the mistake of underrating both the numbers and the abilities of his foes. By great exertions they now had close on half a million of men under arms, near the banks of the Oder and the Elbe, or advancing from Poland and Hungary. True, many of these were reserves or raw recruits, and Colonel Cathcart doubted whether the Austrian reserves were then in existence.[344] But the best authorities place the total at 496,000 men and 1,443 cannon. Moreover, as was agreed on at Trachenberg, 77,000 Russians and 49,000 Prussians now marched from Glatz and Schweidnitz into Bohemia, and speedily came into touch with the 110,000 Austrians now ranged behind the River Eger. The formation of this allied Grand Army was a masterly step. 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 Blücher, 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 Küstrin. 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 Blücher, and then to lead a great force through the Lusatian defiles into Bohemia and drive the allies before him towards Vienna.