It was from Wilna, on the 9th of December, that orders were transmitted to Macdonald, of which a Prussian officer was the bearer, directing him to retreat slowly upon Tilsit. No care was taken to send these instructions by different channels. They did not even think of employing Lithuanians to carry a message of that importance. In this manner the last army, the only one which remained unbroken, was exposed to the risk of destruction. An order, which was written at the distance of only four days' journey from Macdonald, lingered so long on the road, that it was nine days in reaching him.

The marshal directed his retreat on Tilsit, by passing between Telzs and Szawlia. Yorck, with the greatest part of the Prussians, forming his rear-guard, marched at a day's distance from him, in contact with the Russians, and left entirely to themselves. By some this was regarded as a great error on the part of Macdonald; but the majority did not venture to decide, alleging that in a situation so delicate, confidence and suspicion were alike dangerous.

The latter also said that the French marshal did every thing which prudence required of him, by retaining with him one of Yorck's divisions; the other, which was commanded by Massenbach, was under the direction of the French general Bachelu, and formed the vanguard. The Prussian army was thus separated into two corps, Macdonald in the middle, and the one seemed to be a guarantee to him for the other.

At first every thing went on well, although the danger was every where, in the front, in the rear, and on the flanks; for the grand army of Kutusoff had already pushed forward three vanguards, on the retreat of the Duke of Tarentum. Macdonald encountered the first at Kelm, the second at Piklupenen, and the third at Tilsit. The zeal of the black hussars and the Prussian dragoons appeared to increase. The Russian hussars of Ysum were sabred and overthrown at Kelm. On the 27th of December, at the close of a ten hours' march, these Prussians came in sight of Piklupenen, and the Russian brigade of Laskow; without stopping to take breath, they charged, threw it into disorder, and cut off two of its battalions; next day they retook Tilsit from the Russian commander Tettenborn.

A letter from Berthier, dated at Antonowo, on the 14th of December, had reached Macdonald several days before, in which he was informed that the army no longer existed, and that it was necessary that he should arrive speedily on the Pregel, in order to cover KÖnigsberg, and to be able to retreat upon Elbing and Marienburg. This news the marshal concealed from the Prussians. Hitherto the cold and the forced marches had produced no complaints from them; there was no symptom of discontent exhibited by these allies; brandy and provisions were not deficient.

But on the 28th, when General Bachelu extended to the right, towards Regnitz, in order to drive away the Russians, who had taken refuge there after their expulsion from Tilsit, the Prussian officers began to complain that their troops were fatigued; their vanguard marched unwillingly and carelessly, allowed itself to be surprised, and was thrown into disorder. Bachelu, however, restored the fortune of the day, and entered Regnitz.

During this time, Macdonald, who had arrived at Tilsit, was waiting for Yorck and the rest of the Prussian army, which did not make its appearance. On the 29th, the officers, and the orders which he sent them, were vainly multiplied; no news of Yorck transpired. On the 30th, Macdonald's anxiety was redoubled; it was fully exhibited in one of his letters of that day's date, in which, however, he did not yet venture to appear suspicious of a defection. He wrote "that he could not understand the reason of this delay; that he had sent a number of officers and emissaries with orders to Yorck to rejoin him, but that he had received no answer. In consequence, when the enemy was advancing against him, he was compelled to suspend his retreat; for he could not make up his mind to desert this corps, to retreat without Yorck; and yet this delay was ruinous." This letter concluded thus:—"I am lost in conjectures. If I retreat, what would the Emperor say? what would be said by France, by the army, by Europe? Would it not be an indelible stain on the tenth corps, voluntarily to abandon a part of its troops, and without being compelled to it otherwise than by prudence? Oh, no; whatever may be the result, I am resigned, and willingly devote myself as a victim, provided I am the only one:" and he concluded by wishing the French general "that sleep which his melancholy situation had long denied him."

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."

Macdonald saw all at once his force reduced from twenty-nine thousand to nine thousand, but in the state of anxiety in which he had been living for the last two days, any termination to it was a relief.