The situation of the King of Prussia tended to confirm that determination. This unfortunate monarch--well surely did Frederick William then deserve that epithet--was cooped up in the town of Königsberg, only covered by a small army of a few thousand men, and threatened by the gradual approach of the divisions of Ney and Bernadotte; so that the King's personal safety appeared to be in considerable danger. Graudentz, the key of the Vistula, continued indeed to hold out, but the Prussian garrison was reduced to distress, and the hour of surrender seemed to be approaching. To relieve this important fortress, therefore, and at the same time protect Königsberg, were motives added to the other reasons which determined Bennigsen to resume offensive operations. A severe and doubtful skirmish was fought near Mohrungen,[265] in which the French sustained considerable loss. The Cossacks spread abroad over the country, making numerous prisoners; and the scheme of the Russian general succeeded so well, as to enable the faithful L'Estocq to relieve Graudentz with reinforcements and provisions. By these daring operations, Buonaparte saw himself forced into a winter campaign, and issued general orders for drawing out his forces, with the purpose of concentrating them at Willenberg, in the rear of the Russians, (then stationed at Mohrungen,) and betwixt them and their own country. He proposed, in short, to force his enemies eastward towards the Vistula, as at Jena he had compelled the Prussians to fight with their rear turned to the Rhine. Bernadotte had orders to engage the attention of Bennigsen upon the right, and detain him in his present situation, or rather, if possible, induce him to advance eastward towards Thorn, so as to facilitate the operation he meditated. The Russian general learned Buonaparte's intention from an intercepted despatch,[266] and changed his purpose of advancing on Ney and Bernadotte. Marches and counter-marches took place, through a country at all times difficult, and now covered with snow. The experience and dexterity of the French secured some advantages; but these were fully counterbalanced by the daily annoyance and loss which they in turn sustained from Platow and his Cossacks. In cases where the French retreated, the Scythian lances were always on their rear; and when the Russians retired in turn, and were pursued by the French, with the same venturous spirit which they had displayed against others, the latter seldom failed to suffer for their presumption. There was found in the spearmen of the Don and Wolga a natural and instinctive turn for military stratagem, ambuscade, and sudden assault, which compelled the French light troops to adopt a caution, very different from their usual habits of audacity.