From Avesnes, Napoleon wrote to his brother Joseph in the morning:
Avesnes, June 14, 1815, morning
My brother, I move my Imperial Headquarter to Beaumont this evening. Tomorrow the 15th, I will march on Charleroi, where the Prussian army is; this will give way to a battle or the retreat of the enemy. The army is handsome and the weather fine enough; the country support us strongly.
I will write this evening if we must have communications on the 16th. In the meantime, we must prepare.
The Armée du Nord assumed final positions per the Order of the Day given on the 13th.
The IV Corps advanced in the position originally intended for the III Corps, with Bourmont’s division in the lead making at least a 30 kilometer march with Toussaint’s brigade bivouacking at Walcourt and Hulot’s brigade bivouacking at Florennes where Bourmont established his headquarters. Curiously, Bourmont’s division was the only one to get north of Philippeville, despite being closely following by the 12th Division. Bourmont was only a few kilometers from the frontier and only 30 kilometers from Namur, where Blücher had the Prussian Army headquarters.
As we know Bourmont was not hustling to the frontier in order to be first to cross swords with the enemy, it is very curious why at this late stage of the concentration he would perform so diligently for a cause he hated and an army he would soon desert... but as will be revealed soon, Bourmont had quite a different agenda. An agenda only enabled by Soult's order change that left the right column empty... and even had Vandamme's III Corps been ordered back to Philippeville, this corridor would have been open for 36 hours at least.
One bit of recent revisionism to get a lot of support is that Napoleon had not surprised the Allies. And it is true that when one accesses the correspondence, there was a tremendous amount of information about the French army movements.
Peter Hofschröer stated:
Napoleon was clearly unaware of how good the Allied network of spies actually was, and how much the Allies knew of his movements. He based his view on the situation on reports from his spies in Brussels and Namur who reported that all there was quiet. This information was misleading. Although no significant troop movements had taken place, the various Allied headquarters were buzzing with reports coming in from all directions. Napoleon commenced his offensive in the firm belief that he had taken his enemies completely by surprise. This was his first error, and it would not be his only one in this campaign.
It really makes you wonder - why didn't the allies make some of those "significant troop movements," maybe catch the French in the act of crossing the Sambre, and wipe them out piecemeal?
Because they were surprised. Surprised not in a startled type of way, but surprised in the military sense that while the enemy was concentrated and maneuvering, theirs was not.
This analysis that they were not surprised ignores basic facts - there had been a lot of French movements - Wellington as early as April 23rd in a letter to Blücher had said the French army was in continuous motion. There had been lots of deserters. There had been many false alarms. And despite all the information, there was no definitive word on whether Napoleon was going to attack, and if he was, what the line of advance would be. Some in the respective allied headquarters felt military action was imminent, and some did not.
Zieten, commander of I Corps headquartered at Charleroi, reported to Gneisenau his observations of the gathering French army. As a result, according to Lettow Vorbeck:
Hence, the Prussian headquarters had understood the enemy’s intentions. However, they did not think that the attack was imminent and hence were content with informing the corps about the situation and prompting them to make arrangements for a quick gathering. The respective letters were sent to the generals v. Bülow and v. Thielmann on June 14th at noon.
At 11 pm on June 14th, the Allied armies remained in their cantonments. Napoleon's surprise was well under way.