It must not be supposed, however, that these eighteen days passed without military movements of high importance. The reader must remember, that the grand army of Russia was divided into two unequal portions. That commanded under the Emperor by Barclay de Tolly, had occupied Wilna and the vicinity, until the French entered Lithuania, when, by a preconcerted and well-executed retreat, they fell back on their strong fortified camp at Drissa. The smaller army, under Prince Bagration, was much farther advanced to the south-westward, and continued to occupy a part of Poland. The Prince's headquarters were at Wolkowisk; Platoff, with 7000 Cossacks, lay at Grodno, and both he and Bagration maintained communication with the main army through its left wing, which, under Dorokhoff, extended as far as Lida. The army of Bagration had been posted thus far to the south-west, in order that when Napoleon crossed the Niemen, this army might be placed in his rear as he advanced to Wilna. To execute this plan became impossible, so much greater was the invading army than the Russians had anticipated. On the contrary, the French were able to protect the flank of their advance against Wilna by an army of 30,000 men, under the King of Westphalia, placed betwixt them and this secondary Russian army. And far from having it in his power to annoy the enemy, Bagration was placed so much in advance, as greatly to hazard being separated from the main body, and entirely cut off. The Russian prince accordingly had directions from Barclay de Tolly to get his army out of their perilous situation; and again, on the 13th of July, he had orders from Alexander to move on the camp of Drissa. When Napoleon arrived at Wilna, the danger of Bagration became imminent; for the intrenched camp at Drissa was the rendezvous of all the Russian corps, and Napoleon being 150 wersts, or seven days' march, nearer to Drissa than Bagration, neither Napoleon nor any other general had ever so fair an opportunity for carrying into execution the French Emperor's favourite manœuvre, of dividing into two the line of his enemy, which was unquestionably too much extended. It was the 30th of July ere Napoleon was certain of the advantage which he possessed, and he hastened to improve it. He had despatched the greater part of his cavalry under Murat, to press on the retreat of the grand Russian army; the second corps under Oudinot, and the third under Ney, with three divisions of the first corps, were pushed towards the Dwina on the same service, and constituted a force too strong for the army of Barclay de Tolly to oppose. On the right of the army, the King of Westphalia had directions to press upon Bagration in front, and throw him upon the army of Davoust, which was to advance on his flank and towards his rear. It was concluded, that Bagration, cut off from the grand army, and attacked at once by Jerome and Davoust, must necessarily surrender or be destroyed.