Editing Battle of Ligny (section)

==Converging towards battle==
{{Main|Waterloo Campaign: Start of hostilities (15 June)}}
[[File:Ligny-Karte.png|frameless|upright=1.35|right]]
On 15 June Napoleon had crossed the [[Sambre]] at Charleroi and had pushed a wedge between Wellington and Blücher.{{sfn|Esdaile|2016}} His army was divided into three parts: on the left-wing one corps and two cavalry divisions stood under the command of Marshal Ney, on the right-wing two cavalry corps under Marshal Grouchy and in the centre three corps (including the [[Imperial Guard (Napoleon I)|Imperial Guard]]) and [[Édouard Jean-Baptiste Milhaud|Milhaud's]] IV Cavalry Corps ([[cuirassier]]s) as a heavy cavalry reserve under the command of Napoleon. Napoleon's most important goal consisted of keeping the two opposing armies separated and striking each individually. For this purpose, Ney would move against the Anglo-allies on Quatre Bras and hold Wellington's forces there. At the same time the French III Corps under [[Dominique Vandamme|Vandamme]] and IV Corps under [[Étienne Maurice Gérard|Gérard]] would attack the Prussians frontally on their line of defense between [[Wagnelée]], [[Saint-Amand, Fleurus|Saint-Amand]] and [[Ligny]], while Grouchy marched on [[Sombreffe]]. Vandamme's corps was reinforced by [[Jean-Baptiste Girard (soldier)|General Girard]]'s 7th Infantry Division, detached from [[Honoré Charles Reille|Reille's]] II Corps, the bulk of which was at Quatre Bras. Napoleon wanted to advance in the centre of the Prussian position at [[Fleurus]] and decide the battle with a final advance by the [[Old Guard (France)|Old Guard]].  The plan of separation of opposing armies and defeat in detail was an old and favored stratagem of Napoleon's, dating back to his operations in Italy, and had been the deciding factor in his campaigns in Austria, and in his battles with the [[Fifth Coalition]].

Blücher's troops consisted of the I Prussian Corps under [[Hans Ernst Karl, Graf von Zieten|Zieten]], the II Corps under [[George Dubislaw Ludwig von Pirch|Pirch I]]{{efn|name="pirch"}} and the III Corps under [[Johann von Thielmann|Thielmann]]. The I Corps was located in the foremost row and had support from the II Corps standing behind it – the task, the defence of the villages of Ligny, [[Brye]], and Saint-Amand, while the III Corps formed the left wing and the routes of withdrawal while defending [[Gembloux]] and [[Namur]]. Blücher and Wellington had to avoid above all being separated. Still in the morning of the battle Wellington rode to a meeting with Blücher at the windmill of Brye (or Bussy) and promised Blücher the support of at least one Anglo-allied corps.{{sfn|Hofschröer|1999|p=334}} After the break for discussion with Blücher, Wellington left for Quatre Bras.

[[William Siborne]], writing from eyewitness accounts, records it thus: 
{{blockquote| "Upon a calculation being made, however, of the time which would elapse ere the Duke would be able to collect the requisite force for undertaking this operation, and of the possibility of Blucher being defeated before it could be carried into effect, it was considered preferable that Wellington should, if practicable, move to the support of the Prussian Right by the Namur road. But a direct support of this kind was necessarily contingent on circumstances, and subject to the Duke's discretion. The latter having expressed his confident expectation of being enabled to afford the desired support, as also of his succeeding in concentrating, very shortly, a sufficient force to assume the offensive, rode back to Quatre Bras."{{sfn|Siborne|1848|p=136}}}}

In reaction to the troop movements of the French, II and III Corps began sending reinforcements to I Corps under General Ziethen. The Prussian front lines were too long for the troops immediately available and were dependent on the arrival of the IV Corps under [[Friedrich Wilhelm Freiherr von Bülow|Bülow]] advancing from [[Liège]] and the support of the promised Anglo-allied corps.

The Prussians now faced the French with 82,700 troops, with the French Army numbering around 60,800 available troops.{{sfn|Hofschröer|1999|pp=370, 378}}