On the 12th of March news was received at headquarters that Napoleon had received a check before Laon, that Marmont's force had been routed, and that the allied troops were in full march on Paris. The royalists thought that the moment had come for another application to General Werther to induce him to complete the capture. They were anxious to be the first in Burgundy to declare for the Bourbons, and the cautious deliberation of the general of the allied troops exasperated them. He, too, would have liked to get possession of the place before the anticipated cessation of hostilities. He therefore sent another envoy to Colonel Dubois, to give him the latest news of the armies of the coalition, to inform him that the Allies were just about to enter Paris, which was now without defence, and to summon him to surrender in order to avoid a useless effusion of blood; and to say that if he refused to capitulate he must expect rigorous measures, which he, General Werther, would rather avoid, and of which the governor alone would have to bear the responsibility. Colonel Dubois' answer was exactly the same as before. He said he could not capitulate, as his defences remained entire.
During the night of the 12th of March, two mortar batteries were planted on the hill slopes of the right bank, and opened fire in the evening on the faubourg of the left bank. The flèche which served as a tête du pont was broken down by the shells. The German general thought he should thus induce the townspeople to insist on the governor's promptly capitulating. Some of the houses in this faubourg caught fire, and the inhabitants took refuge in the upper town. The garrison could not respond to the fire of the mortar batteries, as they had no more guns of large calibre. The six twenty-four pounders were employed to oppose the enemy's batteries on the north, and they could not disarm the bastions on this side. To complete their distress typhus broke out among the wounded in the cité.
Provisions, too, were becoming scarce, and the garrison was placed on half rations.
On the plateau the cannonade on both sides was continuing, and the escarpments of the two bastions II. and III. were much damaged. As the enemy found nothing more to destroy or burn in the lower town on the right bank, he began his approaches on the 15th of March, and established a demi-parallel with two fresh batteries during the night (of the 15th and following day), of four guns each. This was, however, not accomplished without difficulty, for these batteries were only three hundred yards from the faces of bastions II. and III., whose cavaliers still preserved three guns of large calibre. But on the 18th and 19th of March twenty-six guns were brought to bear against the works, and succeeded in throwing down the parapets and dismounting the guns of the besieged.
During the night of the 19th of March, the colonel endeavoured to mount the cannon that still remained to him; but these pieces of small calibre could effect nothing against the enemy's works. However, the breaches made in the salients of demi-lune No. 2 and of bastion II., were not practicable; and the colonel, wishing to reserve the little artillery he had left, for the moment of assault, retrenched the gorge of bastion II., withdrew its cannon within the fortification and waited the issue. Not to keep his soldiers idle he occupied them at night in trifling sorties which fatigued the besieger. He kept the covered ways in good repair as far as the enemy's fire allowed, and prepared camouflets and chicanes for the moment when the assailant should try to ascend the counterscarp.
On the 25th of March the third parallel was finished. The place was thenceforth only defended by musketry, and a few stone mortars, and grenades, which small sallying parties threw into the trenches at night.
The approaches to crown the covered way and set up breach batteries were advancing but slowly, thanks to the activity of the garrison, whose courage seemed redoubled in seeing the enemy approaching and which defended its glacis foot by foot.
On the 1st of April came the news of the capitulation of Paris, the abdication of the Emperor, and the order to suspend hostilities. The garrison was allowed to retire to Nevers, through Auxonne, Beaune, Autun and Château-Chinon.
On the 5th of April Colonel Dubois quitted La Roche-Pont at the head of seven hundred soldiers of all arms, who were all the able-bodied men left him.