Napoleon leaves Paris to join his army
On 9 June 1815 the final act of the Treaty of Vienna was signed, embodying all the previous separate treaties and reaffirming the Allies intention to force Napoleon from power. By now Napoleon had decided to fight an offensive campaign and, with the Armee du Nord (of some 120,000 men) assembled in northern France, he was ready to strike.
On 12 June Napoleon left Paris to join his army. Escorted by cavalry of the Imperial Guard, he arrived in Avesnes on 13 June. Having failed to reach terms with the Allies, he understood that he could not simply wait for the Russian and Austrian armies to reach the French frontier and invade. Rather, if he could strike a decisive blow against the Prussian and Anglo-Allied armies in the Low Countries, he might be able to split the coalition and drive the British out of the war. This, in turn, would place him in a stronger position to negotiate peace terms with the governments of the Seventh Coalition.
During the early weeks of June the quality of Allied intelligence from France remained variable and while it was clear that Napoleon was intending to move, it was still uncertain where his main line of attack would fall. An advance through Mons or Tournai would first fall on Wellington’s Anglo-Allied army, while an advance through Charleroi would fall on Blücher’s Prussian army.
In a letter to Lord Fitzroy Somerset, on 12 June, Major General Sir William Dornberg provides intelligence regarding the concentration of French forces:
“A French gentleman coming from Maubeuge to join the King, gives the following intelligence. […] The Head Quarters of the army are transferred from Laon to Avesnes, where a division of the Guards is to arrive today. Bonaparte is expected every minute, but nothing certain was known when he had left Paris, where it appears he was still on the 10th. […] He estimates the forces between Philipville, Givet, Mezieres, Guise, and Maubeuge at more than 100,000 troops of the line, a very considerable corps of cavalry was reviewed at Hirson two days ago by Grouchy. The general opinion in the army is that they will attack, and that the arrival of Bonaparte at Avesnes will be the signal for the beginning of hostilities.”
[MS 61 Wellington Papers 1/467/22]
On 14 June, from the Imperial Headquarters at Avesnes, Napoleon made a rousing proclamation to his troops. Drawing on the anniversary of the battles of Marengo and Friedland, it ended with the words: “For every Frenchman with a heart, the time has come to conquer or die!”
That night the French army began its advance across the border into Belgium.