On the same day, he recalled Bachelu and the Prussian cavalry, which was still at Regnitz, to Tilsit.  It was night when Bachelu received the order; he wished to execute it, but the Prussian colonels refused; and they covered their refusal under different pretexts.  “The roads,” they said, “were not passable.  They were not accustomed to make their men march in such dreadful weather, and at so late an hour!  They were responsible to their king for their regiments.”  The French general was astonished, commanded them to be silent, and ordered them to obey; his firmness subdued them, they obeyed, but slowly.  A Russian general had glided into their ranks, and pressed them to deliver up this Frenchman, who was alone in the midst of those who commanded them; but the Prussians, although fully prepared to abandon Bachelu, could not resolve to betray him:  at last they began their march.

At Regnitz, at eight o’clock at night, they had refused to mount their horses; at Tilsit, where they arrived at two in the morning, they refused to alight from them.  At five o’clock in the morning, however, they had all gone to their quarters, and as order appeared to be restored among them, the general went to take some rest.  But the obedience had been entirely feigned, for no sooner did the Prussians find themselves unobserved, than they resumed their arms, went out with Massenbach at their head, and escaped from Tilsit in silence, and by favour of the night.  The first dawn of the last day of the year 1812, informed Macdonald that the Prussian army had deserted him.

It was Yorck, who, instead of rejoining him, deprived him of Massenbach, whom he had just recalled.  His own defection, which had commenced on the 26th of December, was just consummated.  On the 30th of December, a convention between Yorck and the Russian general Dibitch was concluded at Taurogen.  “The Prussian troops were to be cantoned on their own frontiers, and remain neutral during two months, even in the event of this armistice being disapproved of by their own government.  At the end of that time, the roads should be open to them to rejoin the French troops, should their sovereign persist in ordering them to do so.”

Yorck, but more particularly Massenbach, either from fear of the Polish division to which they were united, or from respect for Macdonald, showed some delicacy in their defection.  They wrote to the marshal.  Yorck announced to him the convention he had just concluded, which he coloured with specious pretexts.  “He had been reduced to it by fatigue and necessity; but,” he added, “that whatever judgment the world might form of his conduct, he was not at all uneasy about; that his duty to his troops, and the most mature reflexion, had dictated it to him; that, finally, whatever might be the appearances, he was actuated by the purest motives.”

Massenbach excused himself for his clandestine departure.  “He had wished to spare himself a sensation which his heart felt too painfully.  He had dreaded, lest the sentiments of respect and esteem which he should preserve to the end of his life for Macdonald, should have prevented him from doing his duty.”