He commenced his retreat upon Tilsit, his vanguard consisting of Massenbach's Prussian division, chiefly cavalry, he himself following with the Bavarians, Saxons, &c., and D'Yorck bringing up the rear with 15,000 Prussians, the residue of that auxiliary army. In this order, with the Prussians divided into two corps, and his own posted between them, as if to secure against their combining, the maréchal marched on in sufficient anxiety, but without complaint on his side, or difficulties on that of the Prussian general. But when the maréchal, upon 28th January, arrived at Tilsit, which was in the line of their retreat, and had sent forward the cavalry of Massenbach as far as Regnitz, the troops of D'Yorck in the rear had detached themselves so far that Macdonald was obliged to halt for them. He sent letters to D'Yorck, pressing him to come up--he sent to the cavalry of Massenbach in the van, commanding them to return. From D'Yorck came no answer. At Regnitz, the French general, Bachelu, who had been sent to act as adjutant-general with Massenbach's corps, could find no obedience. The colonels of the Prussian cavalry objected to the weather, and the state of the roads; they would not give the order to sound to horse; and when the horses were at length reluctantly ordered out and produced, the soldiers were equally restive, they would not mount. While the Prussian troops were in this state of mutiny, a Russian emissary was heard to press them to deliver up the Frenchman; but the soldiers, though resolved to leave Bachelu, would not betray him. The proposal shocked their feelings of honour, and they mounted and marched back to Tilsit, to restore Bachelu to Macdonald's army. But their purpose was unchanged. As at Regnitz they had refused to mount their horses, so at Tilsit they refused to alight. At length they were prevailed upon to dismount and retire to their quarters, but it was only a feint; for, shortly after they were supposed asleep, the Prussians mounted in great silence, and, with Massenbach and their officers at their head, marched off to join their countrymen under D'Yorck.